## What is CountVectorizer in NLP?

CountVectorizer tokenizes(tokenization means breaking down a sentence or paragraph or any text into words) the text along with performing very basic preprocessing like removing the punctuation marks, converting all the words to lowercase, etc.

**Why do we use label encoder?**

If you’re new to Machine Learning, you might get confused between these two — Label Encoder and One Hot Encoder. These two encoders are parts of the SciKit Learn library in Python, and they are used to convert categorical data, or text data, into numbers, which our predictive models can better understand.

### What is categorical data in machine learning?

Categorical Data is the data that generally takes a limited number of possible values. All machine learning models are some kind of mathematical model that need numbers to work with. This is one of the primary reasons we need to pre-process the categorical data before we can feed it to machine learning models.

**What is Tfidf Vectorizer?**

TF-IDF is a statistical measure that evaluates how relevant a word is to a document in a collection of documents. This is done by multiplying two metrics: how many times a word appears in a document, and the inverse document frequency of the word across a set of documents.

## How do I encode categorical data in Python?

Another approach is to encode categorical values with a technique called “label encoding”, which allows you to convert each value in a column to a number. Numerical labels are always between 0 and n_categories-1. You can do label encoding via attributes . cat.

**What is Inverse_transform?**

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### Does TfidfVectorizer remove punctuation?

We can use CountVectorizer of the scikit-learn library. It by default remove punctuation and lower the documents. It turns each vector into the sparse matrix. It will make sure the word present in the vocabulary and if present it prints the number of occurrences of the word in the vocabulary.

**What is categorical embedding?**

Embeddings are a solution to dealing with categorical variables while avoiding a lot of the pitfalls of one hot encoding. How do they work? Formally, an embedding is a mapping of a categorical variable into an n-dimensional vector.

## Why do we use MinMaxScaler?

MinMaxScaler(feature_range = (0, 1)) will transform each value in the column proportionally within the range [0,1]. Use this as the first scaler choice to transform a feature, as it will preserve the shape of the dataset (no distortion).

**What is difference between normalization and standardization?**

Normalization typically means rescales the values into a range of [0,1]. Standardization typically means rescales data to have a mean of 0 and a standard deviation of 1 (unit variance).

### Why do we use StandardScaler?

StandardScaler removes the mean and scales each feature/variable to unit variance. This operation is performed feature-wise in an independent way. StandardScaler can be influenced by outliers (if they exist in the dataset) since it involves the estimation of the empirical mean and standard deviation of each feature.

**What does TfidfVectorizer return?**

TfidfVectorizer – Transforms text to feature vectors that can be used as input to estimator. vocabulary_ Is a dictionary that converts each token (word) to feature index in the matrix, each unique token gets a feature index. In each vector the numbers (weights) represent features tf-idf score.

## What is label encoder in Python?

In label encoding in Python, we replace the categorical value with a numeric value between 0 and the number of classes minus 1. If the categorical variable value contains 5 distinct classes, we use (0, 1, 2, 3, and 4). To understand label encoding with an example, let us take COVID-19 cases in India across states.

**What is the use of MinMaxScaler?**

Transform features by scaling each feature to a given range. This estimator scales and translates each feature individually such that it is in the given range on the training set, e.g. between zero and one.

### How do you handle categorical features?

Below are the methods to convert a categorical (string) input to numerical nature:

- Label Encoder: It is used to transform non-numerical labels to numerical labels (or nominal categorical variables).
- Convert numeric bins to number: Let’s say, bins of a continuous variable are available in the data set (shown below).

**What is the difference between normalized scaling and standardized scaling?**

Standardization or Z-Score Normalization is the transformation of features by subtracting from mean and dividing by standard deviation….Difference between Normalisation and Standardisation.

S.NO. | Normalisation | Standardisation |
---|---|---|

8. | It is a often called as Scaling Normalization | It is a often called as Z-Score Normalization. |

## Why is scaling important in machine learning?

Feature scaling is essential for machine learning algorithms that calculate distances between data. Therefore, the range of all features should be normalized so that each feature contributes approximately proportionately to the final distance.

**What is TfidfVectorizer?**

The TfidfVectorizer will tokenize documents, learn the vocabulary and inverse document frequency weightings, and allow you to encode new documents.

### Does scaling remove outliers?

The scaling shrinks the range of the feature values as shown in the left figure below. However, the outliers have an influence when computing the empirical mean and standard deviation. StandardScaler therefore cannot guarantee balanced feature scales in the presence of outliers.

**What is Fit_transform?**

fit_transform() is used on the training data so that we can scale the training data and also learn the scaling parameters of that data. Here, the model built by us will learn the mean and variance of the features of the training set. These learned parameters are then used to scale our test data.

## What is difference between fit and Fit_transform?

In summary, fit performs the training, transform changes the data in the pipeline in order to pass it on to the next stage in the pipeline, and fit_transform does both the fitting and the transforming in one possibly optimized step. “fit” computes the mean and std to be used for later scaling.

**What is StandardScaler?**

StandardScaler. StandardScaler standardizes a feature by subtracting the mean and then scaling to unit variance. Unit variance means dividing all the values by the standard deviation. StandardScaler results in a distribution with a standard deviation equal to 1.

### How do you encode categorical features?

There are many ways to encode categorical variables for modeling, although the three most common are as follows:

- Integer Encoding: Where each unique label is mapped to an integer.
- One Hot Encoding: Where each label is mapped to a binary vector.

**What is the difference between MinMaxScaler and StandardScaler?**

StandardScaler follows Standard Normal Distribution (SND). Therefore, it makes mean = 0 and scales the data to unit variance. MinMaxScaler scales all the data features in the range [0, 1] or else in the range [-1, 1] if there are negative values in the dataset. This range is also called an Interquartile range.

## How do you identify categorical data?

A Test for Identifying Categorical Data

- Calculate the number of unique values in the data set.
- Calculate the difference between the number of unique values in the data set and the total number of values in the data set.
- Calculate the difference as a percentage of the total number of values in the data set.

**Does SVM work with categorical data?**

Non-numerical data such as categorical data are common in practice. Among the three classification methods, only Kernel Density Classification can handle the categorical variables in theory, while kNN and SVM are unable to be applied directly since they are based on the Euclidean distances.

### What is Vectorizer Fit_transform?

1. In a sparse matrix, most of the entries are zero and hence not stored to save memory. The numbers in bracket are the index of the value in the matrix (row, column) and 1 is the value (The number of times a term appeared in the document represented by the row of the matrix). –

**Why is categorical data encoding important?**

Machine learning models require all input and output variables to be numeric. This means that if your data contains categorical data, you must encode it to numbers before you can fit and evaluate a model. Encoding is a required pre-processing step when working with categorical data for machine learning algorithms.