All Learning Algorithms Explained in 14 Minutes
Summary
TLDRDieses Skript bietet eine umfassende Übersicht über maschinelles Lernen, indem es verschiedene Algorithmen erklärt. Es umfasst lineare Regression, Support Vector Machine, Naive Bayes, logistische Regression, K-Nächste-Nachbarn, Entscheidungsbäume, Random Forest, Gradient Boosting, K-Means-Clustering, DBSCAN und PCA. Jeder Algorithmus wird anhand seiner Anwendung, Vorteile und Einschränkungen kurz erläutert, um den Zuhörer einen Einblick in die Welt des maschinellen Lernens zu geben.
Takeaways
- 🤖 Ein Algorithmus ist eine endliche Menge von Anweisungen, die in einer bestimmten Reihenfolge ausgeführt werden, um eine bestimmte Aufgabe auszuführen.
- 📈 Lineare Regression ist ein überwachter Lernalgorithmus, der die Beziehung zwischen einer kontinuierlichen Zielvariable und einer oder mehreren unabhängigen Variablen modelliert.
- 🏠 Support Vector Machine (SVM) ist ein überwachter Lernalgorithmus, der hauptsächlich für Klassifizierungsaufgaben verwendet wird und auch für Regressionsaufgaben geeignet ist.
- 🤖 Naive Bayes ist ein überwachter Lernalgorithmus für Klassifizierungsaufgaben, der auf der Annahme beruht, dass Merkmale unabhängig voneinander sind.
- 📊 Logistic Regression ist ein überwachter Lernalgorithmus, der hauptsächlich für binäre Klassifizierungsprobleme verwendet wird und die Sigmoid-Funktion nutzt, um eine Klassifizierung durchzuführen.
- 👫 K-Nächste-Nachbarn (KNN) ist ein überwachter Lernalgorithmus, der sowohl für Klassifizierung als auch für Regressionsaufgaben eingesetzt werden kann und die Werte von Datenpunkten anhand der umliegenden Datenpunkte bestimmt.
- 🌳 Entscheidungsbäume arbeiten durch iteratives Fragen, um Daten zu partitionieren und versuchen, die Klassifizierbarkeit zu maximieren.
- 🌲 Random Forest ist eine Ensemble-Methode aus vielen Entscheidungsbäumen, die das Bagging-Verfahren verwendet, um eine höhere Genauigkeit zu erreichen als ein einzelner Entscheidungsbaum.
- 🌟 Gradient Boosted Decision Trees (GBDT) ist ein Ensemble-Algorithmus, der Boosting-Methoden verwendet, um einzelne Entscheidungsbäume zu kombinieren und einen starken Lernenden aus vielen schwachen Lernenden zu erstellen.
- 🔢 K-Means-Clustering ist eine unüberwachte Lernmethode, die Datenpunkte in K Gruppen partitioniert, sodass Datenpunkte in derselben Gruppe ähnlich sind und in verschiedenen Gruppen unterschiedlich sind.
- 🌐 DBSCAN ist eine dichte basierte Clustering-Technik, die beliebig geformte Cluster und Rauschen erkennen kann, ohne eine voreingestellte Anzahl von Clustern anzugeben.
- 📉 PCA (Principal Component Analysis) ist ein Dimensionsreduktionsalgorithmus, der neue Merkmale aus vorhandenen Merkmalen ableitet, um die Varianz im ursprünglichen Datensatz so gut wie möglich zu erklären.
Q & A
Was ist ein Algorithmus?
-Ein Algorithmus ist eine endliche Menge von Anweisungen, die in einer bestimmten Reihenfolge ausgeführt werden, um eine bestimmte Aufgabe auszuführen. Es ist nicht ein vollständiges Programm oder Code, sondern einfache Logik zu einem Problem.
Was versucht ein lineares Regressionsmodell?
-Ein lineares Regressionsmodell versucht, eine lineare Beziehung zwischen einer kontinuierlichen Zielvariable und einer oder mehreren unabhängigen Variablen durch Anpassung einer linearen Gleichung an die Daten zu modellieren.
Wie wird die beste Regressionslinie in einem linearen Regressionsmodell bestimmt?
-Die beste Regressionslinie wird durch Minimierung der Summe der Quadrate der Abstände zwischen den Datenpunkten und der Regressionslinie bestimmt.
Was ist Support Vector Machine (SVM) und wofür wird es verwendet?
-Support Vector Machine (SVM) ist ein überwachter Lernalgorithmus, der hauptsächlich für Klassifizierungsaufgaben verwendet wird, ist aber auch für Regressionsaufgaben geeignet. SVM unterscheidet Klassen, indem sie eine Entscheidungsgrenze zeichnet.
Wie wird die Entscheidungsgrenze in SVM bestimmt?
-Die Entscheidungsgrenze in SVM wird so bestimmt, dass die Distanz zu den Support-Vektoren maximiert wird, um eine gute Allgemeinheit und Robustheit gegenüber Rauschen zu gewährleisten.
Was ist der Unterschied zwischen Naive Bayes und anderen Klassifikatoren?
-Naive Bayes ist ein Klassifikator, der annimmt, dass alle Merkmale voneinander unabhängig sind. Dies ist im Gegensatz zu anderen Klassifikatoren, die möglicherweise Korrelationen zwischen Merkmalen berücksichtigen.
Was ist die Basis des Logistic Regression?
-Die Basis des Logistic Regression ist die Logistic-Funktion, auch Sigmoid-Funktion genannt, die einen reellen Zahlenwert in einen Wert zwischen 0 und 1 abbildet und für binäre Klassifizierungsaufgaben verwendet wird.
Wie funktioniert K-Nächste-Nachbarn (KNN)?
-K-Nächste-Nachbarn ist ein Algorithmus, der bei Klassifikations- und Regressionsaufgaben verwendet wird. Der Wert eines Datenpunktes wird durch die Werte seiner K nächsten Nachbarn bestimmt, entweder durch Mehrheitsabstimmung (Klassifikation) oder durchschnittliche Werte (Regression).
Was ist der Hauptvorteil von Entscheidungsbäumen?
-Entscheidungsbäume haben den Vorteil, dass sie iterativ Fragen stellen, um Daten zu partitionieren, was es einfach macht, die Datenpartitionierung visuell zu repräsentieren und zu verstehen.
Was ist Random Forest und wie unterscheidet es sich von einzelnen Entscheidungsbäumen?
-Random Forest ist ein Ensemble aus vielen Entscheidungsbäumen, die mit der Methode des Baggings erstellt werden. Im Gegensatz zu einzelnen Entscheidungsbäumen reduziert Random Forest das Risiko des Überanpassens und bietet in der Regel eine höhere Genauigkeit.
Was ist Gradient Boosted Decision Trees (GBDT) und wie funktioniert es?
-GBDT ist ein Ensemble-Algorithmus, der Boosting-Methoden verwendet, um einzelne Entscheidungsbäume zu kombinieren. Jeder Baum versucht, die Fehler des vorherigen Baumes zu minimieren, was zu einem hocheffizienten und genauen Modell führt.
Was ist K-Means-Clustering und wie funktioniert es?
-K-Means-Clustering ist eine unüberwachte Lernmethode, die Datenpunkte in K Cluster partitioniert, so dass Datenpunkte im selben Cluster ähnlich sind und diejenigen in verschiedenen Clustern weiter auseinander liegen.
Was ist DBSCAN und wie unterscheidet es sich von K-Means?
-DBSCAN, für Density-Based Spatial Clustering of Applications with Noise, ist in der Lage, beliebig geformte Cluster und Rauschen zu erkennen. Im Gegensatz zu K-Means muss die Anzahl der Cluster nicht vorab bekannt sein und es ist robust gegenüber Ausreißern.
Was ist Principal Component Analysis (PCA) und was ist ihr Hauptzweck?
-PCA ist ein Dimensionsreduktionsalgorithmus, der neue Features aus vorhandenen ableitet, um die Varianz im ursprünglichen DataSet so gut wie möglich beizubehalten, während die Anzahl der Features reduziert wird.
Outlines
🤖 Maschinelles Lernen: Grundlegende Algorithmen
Dieses Abschnitt erklärt grundlegende Konzepte des maschinellen Lernens, darunter die Bedeutung von Algorithmen, die Art der Supervised Learning-Algorithmen wie Lineare Regression, Support Vector Machine (SVM), Naive Bayes und Logistic Regression. Es geht auch auf die K-Nearest Neighbors (KNN) ein, die für Klassifizierungs- und Regressionsaufgaben eingesetzt werden. Jeder Algorithmus wird anhand seiner Funktionsweise und Anwendungsfälle detailliert beschrieben.
🌳 Entscheidungsbäume und Ensemble-Methoden
In diesem Abschnitt werden Entscheidungsbäume als iteratives Fragen-Stellen-Verfahren vorgestellt, das zur Datenpartitionierung verwendet wird. Es wird erklärt, wie Entscheidungsbäume anhand von Splits zunehmend informativ werden und wie man sie vermeiden kann, in Overfitting zu geraten. Der Abschnitt führt auch in Random Forests und Gradient Boosted Decision Trees (GBDT) als Ensemble-Methoden ein, die mehrere Entscheidungsbäume verwenden, um eine robustere Vorhersage zu erzielen. Dabei werden die Vor- und Nachteile dieser Methoden diskutiert.
🔍 Clustering und Dimensionsreduktion
Der dritte Abschnitt konzentriert sich auf Clustering- und Dimensionsreduktion-Techniken. K-Means-Clustering, ein Partitionsbasiertes Verfahren, das Datenpunkte in Cluster gruppiert, wird erläutert. Es folgen DBSCAN und andere Techniken, die für Daten mit nicht-linearer Struktur oder zur Detektion von Ausreißern geeignet sind. Schließlich wird die Prinzipal-Komponenten-Analyse (PCA) als Methode zur Reduktion der Datendimensionalität vorgestellt, die neue Features ableitet, um die Varianz im Datensatz zu maximieren.
Mindmap
Keywords
💡Algorithmus
💡Lineare Regression
💡Support Vector Machine (SVM)
💡Naive Bayes
💡Logistische Regression
💡K-Nächste-Nachbarn (KNN)
💡Entscheidungsbaum
💡Random Forest
💡Gradient Boosted Decision Trees (GBDT)
💡K-Means-Clustering
💡DBSCAN
💡Prinzipalkomponentenanalyse (PCA)
Highlights
Algorithms are defined as a finite set of instructions to perform a specific task.
Linear regression models the relationship between a continuous target variable and one or more independent variables.
Support Vector Machine (SVM) is used for classification and regression tasks by drawing a decision boundary.
Naive Bayes classifier assumes feature independence and uses Bayes' theorem for classification.
Logistic regression is used for binary classification problems using the logistic or sigmoid function.
K-Nearest Neighbors (KNN) determines the class of a data point based on the majority class of its neighbors.
Decision trees partition data by asking questions that increase the purity of nodes.
Random Forest is an ensemble of decision trees that reduces the risk of overfitting.
Gradient Boosted Decision Trees (GBDT) combines decision trees sequentially to minimize errors of previous trees.
K-means clustering groups data points into clusters based on similarities.
DBSCAN clustering finds arbitrary shaped clusters and is robust to outliers.
Principal Component Analysis (PCA) is a dimensionality reduction technique that derives new features from existing ones.
SVM is effective when the number of dimensions exceeds the number of samples.
Naive Bayes is fast due to its independence assumption but less accurate for correlated features.
Logistic regression maps any real-valued number to a value between 0 and 1 for binary classification.
KNN's performance is sensitive to the choice of K, affecting its generalization and sensitivity to noise.
Decision trees are prone to overfitting and benefit from ensemble methods like Random Forest.
GBDT is efficient for both classification and regression, requiring careful hyperparameter tuning.
K-means requires a predetermined number of clusters and may not be suitable for nonlinear data structures.
DBSCAN does not require a predefined number of clusters and can detect outliers.
PCA retains significant variance of the original dataset using fewer features.
Transcripts
every single machine learning algorithm
explained in case you don't know an
algorithm is a set of commands that must
be followed for a computer to perform
calculations or like other
problemsolving operations according to
its formal definition an algorithm is a
finite set of instructions carried out
in a specific order to perform a
particular task it's not an entire
program or code it is simple logic to a
problem linear regression is a
supervised learning algorithm and tries
to model their relationship between a
continuous Target variable and one or
more independent VAR variables by
fitting a linear equation to the data
take this chart of dots for example a
linear regression model tries to fit a
regression line to the data points that
best represents the relations or
correlations with this method the best
regression line is found by minimizing
the sum of squares of the distance
between the data points and the
regression line so for these data points
the regression line Looks like this
support Vector machine or svm for short
is a supervised learning algorithm and
is mostly used for classification tasks
but is also suitable for regression R
tasks svm distinguishes classes by
drawing a decision boundary how to draw
or determine the decision boundary is
the most critical part in svm algorithms
before creating the decision boundary
each observation or data point is
plotted in N dimensional space with n
being the number of features used for
example if we use length and width to
classify different cells observations
are plotted in a two-dimensional space
and decision boundary is a line if we
use three features decision boundary is
a plane in three-dimensional space if we
use more than three features decision
boundary becomes a hyper plane which is
really hard to visualize decision
boundary is drawn in a way that the
distance to support vectors are
maximized if the decision boundary is
too close to a support Vector it'll be
highly sensitive to noises and not
generalize well even very small changes
to independent variables may cause a
misclassification svm is especially
effective in cases where number of
dimensions are more than the number of
samples when finding the decision
boundary svm uses a subset of training
points rather than all points which
makes it memory efficient on the other
hand training time increases for large
data sets which negatively affects the
performance Nave Bas is a supervised
learning algorithm used for
classification tasks hence it is also
called Nave Bas classifier Nave Bas
assumes that features are independent of
each other and there is no correlation
between features however this is not the
case in real life this Nave Assumption
of features being uncorrelated is the
reason why this algorithm is called
naive the intuition behind naive Bay
algorithm is the Bas theorem p a is the
probability of event a given event B has
already occurred PBA is probability of
event B given event a has already
occurred PA is the probability of event
a and PB is the probability of event B
naive Bas classifier calculates the
probability of a class given a set of
feature values the the assumption that
all features are independent makes knif
based algorithm very fast when compared
to complicated algorithms in some cases
speed is preferred over higher accuracy
but on the other hand the same
assumption makes knife Bas algorithm
less accurate than complicated
algorithms logistic regression is a
supervised learning algorithm which is
mostly used for binary classification
problems logistic regression is a simple
yet very effective classification
algorithm so it is commonly used for
many binary classification tasks things
like customer turn spam email website or
ad click predictions are some examples
of the areas where logistic regression
offers a powerful solution the basis of
logistic regression is the logistic
function also called the sigmoid
function which takes any real value
number and Maps it to a value between 0o
and 1 Let's consider we have the
following linear equation to solve
logistic regression model takes a linear
equation as input and uses logistic
function and log odds to perform a
binary classification task then we will
get the f famous shaped graph of
logistic regression we can use the
calculated probability as is for example
the output can be the probability that
this email is Spam is 95% or the
probability that the customer will click
on the ad is 70% however in most cases
probabilities are used to classify data
points for example if the probability is
greater than 50% the prediction is
positive class or one otherwise the
prediction is negative class or zero K
nearest Neighbors or K&N for short is a
supervised learning algorithm that can
be used to solve both classification and
regression tasks the main idea behind
KNN is that the value of a class or of a
data point is determined by the data
points around it KNN classifier
determines the class of a data point by
majority voting principle for instance
if K is set to five the classes of five
closest points are checked prediction is
done according to the majority class
similarly K&N regression takes the mean
value of five CL closest points let's go
over an example consider the following
data points that belong to four
different classes and let's see how the
predicted classes change according to
the K value it is very important to
determine an optimal K value if K is too
low the model is too specific and not
generalized well it also tends to be too
sensitive to noise the model
accomplishes a high accuracy on train
set but will be a poor predictor on new
previously unseen data points therefore
we are likely to end up with an overfit
model on the the other hand if K is too
large the model is too generalized and
is not a good predictor on both train
and test sets this situation is known as
underfitting KNN is simple and easy to
interpret it does not make any
assumption so it can be implemented in
nonlinear tasks KNN does become very
slow as number of data points increases
because the model needs to store all
data points thus it is not memory
efficient another downside of KNN is
that it is sensitive to outliers
decision trees work by iteratively
asking questions to partition data it is
easier to conceptualize the partitioning
data with a visual representation of a
decision tree this represents a decision
tree to predict customer CH first split
is based on monthly charges amount then
the algorithm keeps asking questions to
separate class labels the question get
more specific as the tree gets deeper
the aim is to increase the
predictiveness as much as possible at
each partitioning so that the model
keeps gaining information about the data
set randomly splitting the feature does
not usually give us the valuable insight
into the data set it's the splits that
increase purity of nodes that are most
informative the purity of a node is
inversely proportional to the
distribution of different classes in
that node the questions to ask are
chosen in a way that increases Purity or
decreases impurity but how many
questions do we ask when do we stop when
is our tree sufficient to solve our
classification problem the answer to all
of these questions leads us to one of
the most important Concepts in machine
learning overfitting the model can keep
asking questions until all nodes are
pure however this would be a two
specific model and would not generalize
will it achieves high accuracy with
training set but performs poorly on new
previously unseen data points which
indicates overfitting decision tree
algorithm usually does not require to
normalize or scale features it is also
suitable to work on a mixture of feature
data types on the negative side it is
prone to overfitting and needs to be
ensembled in order to generalize well
random Forest is an ensemble of many
decision trees random forests are built
using a method called bagging in which
decision trees are used as par parel
estimators if used for a classification
problem the result is based on majority
vote of the results received from each
decision tree for regression the
prediction of a leaf node is the mean
value of the target values in that leaf
random Forest regression takes mean
values of results from decision trees
random forests reduce the risk of
overfitting and accuracy is much higher
than a single decision tree furthermore
decision trees in a random forest run in
parallel so that the time does not
become a bottleneck the success of a
random Forest highly depends on using
uncorrelated decision trees if we use
the same or very similar trees the
overall result will not be much
different than the result of a single
decision tree random forests achieve to
have uncorrelated decision trees by
bootstrapping and feature Randomness
bootstrapping is randomly selecting
samples from training data with
replacement they are called the
bootstrap samples feature Randomness is
achieved by selecting features randomly
for each decision Tree in a random
Forest the number of features used for
each tree in a random Forest can be
controlled with maxcore features
parameter random Forest is a highly
accurate model on many different
problems and does not require
normalization or scaling however it is
not a good choice for high dimensional
data sets compared to fast linear models
gradient boosted decision trees or gbdt
for short is an ensemble algorithm which
uses boosting methods to combine
individual decision trees boosting means
combining a learning algorithm in series
to achieve a strong learner from many
sequentially connect weak Learners in
the case of gbdt the weak Learners are
the decision trees each tree attempts to
minimize the errors of previous tree
trees in boosting are weak learners but
adding many trees in series and each
focusing on the errors from the previous
one make boosting a highly efficient and
accurate model unlike bagging boosta
does not involve bootstrap sampling
every time a new tree is added it fits
on a modified version of the initial
data set since trees are added
sequentially boosting algorithms learn
slowly in statistical learning models
that learn slowly perform better gbdt is
very efficient on both classification
and regression tasks and provides more
accurate predictions compared to random
Forest it can handle mixed type of
features and no pre-processing is needed
gbdt does require careful tuning of
hyperparameters in order to prevent the
model from overfitting K means
clustering clustering is a way to group
a set of data points in a way that
similar data points are grouped together
therefore clustering algorithms look for
similarities or dissimilarities among
data points clustering is an
unsupervised learning method so there is
no label associated with data points
clustering algorithms try to find the
underlying structure of the data
observations or data points in a
classification task have labels each
observation is classified according to
some measurements classification
algorithms try to model the relationship
between measurements on observations and
their assigned class then the model
predicts the class of new observations K
means clustering aims to partition data
into K clusters in a way that data
points in the same cluster are similar
and data points in different clusters
are further apart thus it is a partition
based clustering technique similarity of
two points is determined by the distance
between them consider the following 2D
visualization of a data set it can be
partied into four different clusters now
real life data sets are much more
complex in which clusters are not
clearly separated however the algorithm
works in the same way K means is an
iterative process it is built on
expectation maximization algorithm after
the number of clusters are determined it
works by executing the following steps
number one it randomly selects the
centroids or the center of cluster for
each cluster then it calculates the
distance of all data points to the
centroids it assigns the data points to
the closest cluster it finds the new
centroids of each cluster by taking the
mean of all data points in the cluster
and it repeats steps 2 3 and four until
all points converge and cluster Center
stop moving K means clustering is
relatively fast and easy to interpret it
is also able to choose the positions of
initial centroids in a smart way that
speeds up the convergence the one
challenge with K means is that the
number of clusters must be predetermined
cayman's algorithm is not able to guess
how many clusters exist in the data if
there is a nonlinear structure
separating groups in the data K means
will not be a good choice DB scan
clustering partition based and
hierarchical clustering techniques are
highly efficient with normal shaped
clusters however when it comes to
arbitrary shaped clusters or detecting
outliers density based techniques are
more efficient DB scan stands for
density based spatial clustering of
applications with noise it is able to
find arbitrary shaped clusters and
clusters with noise the main idea behind
DB scan is that a point belongs to a
cluster if it is close to many points
from that cluster there are two key
parameters of DB scan EPS which is the
distance that specifies the neighborhood
two points are considered to be
neighbors if the distance between them
are less than or equal to EPs and Min
pts which is the minimum number of data
points to define a cluster based on
these two parameters points are
classified as score Point border point
or outlier a point is a core point if
there are at least Min pts number of
points including the point itself in its
surrounding area with radius EPS a point
is a border point if it is unreachable
from a core point and there are less
than Min pts number of points within its
surrounding area and a point is an
outlier if it is not a core point and
not reach from any core points DB scan
does not require to specify a number of
clusters beforehand it is robust to
outliers and able to detect the outliers
in some cases determining an appropriate
distance of neighborhood EPS is not easy
and it requires domain knowledge
principle components analysis or PCA is
a dimensionally reduction algorithm
which basically derives new features
from the existing ones with keeping as
much information as possible PCA is an
unsupervised learning algorithm but it
is also widely used as a pre-processing
step for supervised learning algorithms
PCA deres new features by finding the
relations among features in a data set
the aim of PCA is to explain the
variance within the original data set as
much as possible by using less features
the new derived features are called
principal components the order of
principal components is determined
according to the fraction of variance of
original data set they explain the
advantage of PCA is that a significant
amount of variance of the original data
set is retained using much smaller
number of features than the original
data set principal components are
ordered according to the amount of
variants that they explain and that is
every common machine learning algorithm
explained
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