# Questions tagged [multi-class]

Multiclass classification is a classification task in which there are more than two classes. It is also called multinomial classification.

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### How to compute precision/recall for multiclass-multilabel classification?

I'm wondering how to calculate precision and recall measures for multiclass multilabel classification, i.e. classification where there are more than two labels, and where each instance can have ...
176k views

### How do you calculate precision and recall for multiclass classification using confusion matrix?

I wonder how to compute precision and recall using a confusion matrix for a multi-class classification problem. Specifically, an observation can only be assigned to its most probable class / label. I ...
76k views

### What is the difference between Multiclass and Multilabel Problem

What is the difference between a multiclass problem and a multilabel problem?
17k views

### Best way to perform multiclass SVM

I know that the SVM is a binary classifier. I would like to extend it to multi-class SVM. Which is the best, and maybe the easiest, way to perform it? code: in MATLAB ...
7k views

### Micro vs weighted F1 score

In a multi-label or multi-class classification setting, when choosing between a micro or a weighted F1 score, what shall I take into account? The main upside of choosing macro is that one gets a ...
8k views

### How to handle the difference between the distribution of the test set and the training set?

I think one basic assumption of machine learning or parameter estimation is that the unseen data come from the same distribution as the training set. However, in some practical cases, the distribution ...
5k views

### What is the difference between a multi-label and a multi-class classification?

What is the difference between multi-label classification and multiclass classfication. Speficially, what is the difference between a label and a class? Please provide a clear example. "Multiclass ...
23k views

### Multi-class logarithmic loss function per class

In a multi-classification problem, we define the logarithmic loss function $F$ in terms of the logarithmic loss function per label $F_i$ as:  F = -\frac{1}{N}\sum_{i}^{N}\sum_{j}^{M}y_{ij} \cdot Ln(...
5k views

### How to threshold multiclass probability prediction to get confusion matrix?

Lets say my multinomial logistic regression predict that a chance of a sample belonging to a each class is A=0.6, B=0.3, C=0.1 How do I threshold this values to get just binary prediction of a sample ...
3k views

### How do I use negative examples (in addition to positive ones) for training a multiclass softmax classifier (or a neural net with softmax output)?

Suppose we are training a neural network for multi-class classification, and we use softmax (or hierarchical softmax) as its output layer. For positive examples, we need to maximize the log ...
224 views

### Training N classifiers for N labels vs one classifier with N labels

I have a classification problem which is multi-label with N labels. I would like to know which method would be the better choice? Training N classifiers (1 for each label) or a single classifier which ...
1k views

### How to build ROC curve (or AUC) of classification model from confusion matrix only

I've been looking into using ROC curves as a evaluation tool of a multi-class classification. The only data I have about this classification is in form of 7-by-7 confusion matrix. Visualisation of ...
42k views

### How to determine the quality of a multiclass classifier

Given a dataset with instances $x_i$ together with $N$ classes where every instance $x_i$ belongs exactly to one class $y_i$ a multiclass classifier After the training and testing I basically have a ...
10k views

### Extending 2-class models to multi-class problems

This paper on Adaboost gives some suggestions and code (page 17) for extending 2-class models to K-class problems. I would like to generalize this code, such that I can easily plug in different 2-...
5k views

### How the probability threshold of a classifier can be adjusted in case of multiple classes? [duplicate]

The above is a very simple example of having a probability classifier output for a binary-class case either 0 or 1 based on some probabilities. In addition it is straightforward how you can change the ...
20k views

### Output of Scikit SVM in multiclass classification always gives same label

I am currently using Scikit learn with the following code: ...
5k views

### Multi-label or multi-class…or both?

I'm having a hard time getting the difference between multi-class and multi-label classification with CNNs. My understanding is that if I want to classify different breeds of dogs, that is a multi-...
1k views

### How to include negative examples in multi-class classification?

I have a problem similar to this question: How do I use negative examples (in addition to positive ones) for training a multiclass softmax classifier (or a neural net with softmax output)? where I ...
2k views

### Probability calibration metric for multiclass classifier

A machine learning classifier can be calibrated so that when the probability that datapoint i is of class A is 0.6, this is true 60% of the time. In the binary class setting, this can be visualised ...
4k views

### Softmax regression or $K$ binary logistic regression

For a multi-class classification problem, we can use $K$ binary logistic classifiers, or one softmax regression classifier, so how to make the choice between the two? IMHO, the $K$ binary logistic ...
2k views

### Why do one-versus-all multi class SVMs need to be calibrated?

On the wiki page for multi-class support vector machines (https://en.wikipedia.org/wiki/Support_vector_machine#Multiclass_SVM) it states that "it is important that the output functions be calibrated ...
15k views

### Logistic Regression for non-binary classification (multi-class) in R

I am trying to use glm(family = binomial(link = 'logit')) for a classification task with 14 classes. I know that logistic regression is used in R for binary ...
996 views

### Are the total false positives and false negatives of a large confusion matrix equal?

I have a confusion matrix which is 20x20 that is the product of a random forest classification of ~20k instances. Each of these instances was put into a specific class where rows are actual class and ...
470 views

### Evaluating Unbalanced Multiclass Classifiers: Which Tests to Use? [closed]

I am looking for some comprehensive instructions and ideally out of the box solutions (ideally for python) for evaluating different classifiers (which are already trained) for a multiclass ...
5k views

### How can I derive confidence intervals from the confusion matrix for a classifier?

I have am using k-fold cross validation to generate a confusion matrix for a classifier. I need to calculate 95% confidence intervals for the number of times each class is predicted when run against a ...
974 views

### Calibrating multiple binary SVM classifiers for one-vs-all multi-class classification

I'm classifying text using the one-vs-all approach. There are three classes. I've trained 3 different binary SVM classifiers using 10-fold cross-validation. The accuracy of the binary classifiers ...
184 views

### Streaming multi-class classification with growing number of classes

I'm looking for some references for online multi-class classification problem where the number of classes grows over time. Concretely, the data at time-step $t$ comes in the form \$\left(\mathbf{x}_t, ...
4k views

### Calculate accuracy using true/false positives/negatives

I got predicted = [0, 0, 1, 0, 1, 2, 1, 0, 1, 0] actual = [1, 2, 1, 2, 0, 1, 0, 2, 1, 1] from multiclass classifier Next, I calculate for 3 classes ...
988 views

### How to combine/aggregate classification accuracies from binary one-vs-one classifiers to get final accuracy equivalent a multiclass classifier?

Consider a 3 class data, say, Iris data. Suppose we want do binary SVM classification for this multiclass data using Python's sklearn. So we have the following ...
619 views

### Which is the best classifier and with what performance measures?

I tried to implement a Classifier comparison like in the scikit-learn for text classification. I used an 81 instances as a training sample and a 46 instances as a test sample. I tried several ...
24 views

### Multiclass classification vs Binary classification with class merging: prediction accuracy

I have a dataset with 4 labels. For me the most important is to be able to distinguish label 1 from all other labels, I don't care that much about distinguishing between labels 2,3 and 4. The ...