What is Label Encoding in Python


Label encoding is a method utilized in machine studying and information evaluation to transform categorical variables into numerical format. It’s notably helpful when working with algorithms that require numerical enter, as most machine studying fashions can solely function on numerical information. On this rationalization, we’ll discover how label encoding works and easy methods to implement it in Python.

Let’s contemplate a easy instance with a dataset containing details about several types of fruits, the place the “Fruit” column has categorical values reminiscent of “Apple,” “Orange,” and “Banana.” Label encoding assigns a singular numerical label to every distinct class, reworking the explicit information into numerical illustration.

To carry out label encoding in Python, we will use the scikit-learn library, which gives a variety of preprocessing utilities, together with the LabelEncoder class. Right here’s a step-by-step information:

  1. Import the required libraries:
pythonCopy codefrom sklearn.preprocessing import LabelEncoder
  1. Create an occasion of the LabelEncoder class:
pythonCopy codelabel_encoder = LabelEncoder()
  1. Match the label encoder to the explicit information:
pythonCopy codelabel_encoder.match(categorical_data)

Right here, categorical_data refers back to the column or array containing the explicit values you need to encode.

  1. Rework the explicit information into numerical labels:
pythonCopy codeencoded_data = label_encoder.remodel(categorical_data)

The remodel methodology takes the unique categorical information and returns an array with the corresponding numerical labels.

  1. If wanted, you too can reverse the encoding to acquire the unique categorical values utilizing the inverse_transform methodology:
pythonCopy codeoriginal_data = label_encoder.inverse_transform(encoded_data)

Label encoding will also be utilized to a number of columns or options concurrently. You may repeat steps 3-5 for every categorical column you need to encode.

You will need to observe that label encoding introduces an arbitrary order to the explicit values, which can result in incorrect assumptions by the mannequin. To keep away from this difficulty, you possibly can think about using one-hot encoding or different strategies reminiscent of ordinal encoding, which offer extra applicable representations for categorical information.

Label encoding is an easy and efficient approach to convert categorical variables into numerical kind. By utilizing the LabelEncoder class from scikit-learn, you possibly can simply encode your categorical information and put together it for additional evaluation or enter into machine studying algorithms.

Now, allow us to first briefly perceive what information sorts are and its scale. You will need to know this for us to proceed with categorical variable encoding. Knowledge could be categorised into three sorts, particularly, structured information, semi-structured, and unstructured information

Structured information denotes that the info represented is in matrix kind with rows and columns. The info could be saved in database SQL in a desk, CSV with delimiter separated, or excel with rows and columns.

The info which isn’t in matrix kind could be categorised into semi-Structured information (information in XML, JSON format) or unstructured information (emails, photographs, log information, movies, and textual information).

Allow us to say, for given information science or machine studying enterprise drawback if we’re coping with solely structured information and the info collected is a mix of each Categorical variables and Steady variables, a lot of the machine studying algorithms won’t perceive, or not be capable to cope with categorical variables. Which means, that machine studying algorithms will carry out higher when it comes to accuracy and different efficiency metrics when the information is represented as a quantity as an alternative of categorical to a mannequin for coaching and testing. 

Deep studying strategies such because the Synthetic Neural community anticipate information to be numerical. Thus, categorical information should be encoded to numbers earlier than we will use it to suit and consider a mannequin.

Few ML algorithms reminiscent of Tree-based (Resolution Tree, Random Forest ) do a greater job in dealing with categorical variables. The very best apply in any information science undertaking is to rework categorical information right into a numeric worth. 

Now, our goal is evident. Earlier than constructing any statistical fashions, machine studying, or deep studying fashions, we have to remodel or encode categorical information to numeric values. Earlier than we get there, we’ll perceive several types of categorical information as under.

Nominal Scale

The nominal scale refers to variables which are simply named and are used for labeling variables. Word that each one of A nominal scale refers to variables which are names. They’re used for labeling variables. Word that each one of those scales don’t overlap with one another, and none of them has any numerical significance. 

Beneath are the examples which are proven for nominal scale information. As soon as the info is collected, we should always often assign a numerical code to symbolize a nominal variable.

For instance, we will assign a numerical code 1 to symbolize Bangalore, 2 for Delhi, 3 for Mumbai, and 4 for Chennai for a categorical variable- during which place do you reside. Necessary to notice that the numerical worth assigned doesn’t have any mathematical worth connected to them. Which means, that fundamental mathematical operations reminiscent of addition, subtraction, multiplication, or division are pointless. Bangalore + Delhi or Mumbai/Chennai doesn’t make any sense.

Ordinal Scale

An Ordinal scale is a variable during which the worth of the info is captured from an ordered set. For instance, buyer suggestions survey information makes use of a Likert scale that’s finite, as proven under.

On this case, let’s say the suggestions information is collected utilizing a five-point Likert scale. The numerical code 1, is assigned to Poor, 2 for Honest, 3 for Good, 4 for Very Good, and 5 for Glorious. We are able to observe that 5 is healthier than 4, and 5 is significantly better than 3. However when you take a look at glorious minus good, it’s meaningless. 

We very nicely know that almost all machine studying algorithms work completely with numeric information. That’s the reason we have to encode categorical options right into a illustration appropriate with the fashions. Therefore, we’ll cowl some well-liked encoding approaches:

  • Label encoding
  • One-hot encoding
  • Ordinal Encoding

Label Encoding

In label encoding in Python, we change the explicit worth with a numeric worth between 0 and the variety of lessons minus 1. If the explicit variable worth incorporates 5 distinct lessons, we use (0, 1, 2, 3, and 4).

To know label encoding with an instance, allow us to take COVID-19 circumstances in India throughout states. If we observe the under information body, the State column incorporates a categorical worth that’s not very machine-friendly and the remainder of the columns include a numerical worth. Allow us to carry out Label encoding for State Column.

From the under picture, after label encoding, the numeric worth is assigned to every of the explicit values. You could be questioning why the numbering shouldn’t be in sequence (High-Down), and the reply is that the numbering is assigned in alphabetical order. Delhi is assigned 0 adopted by Gujarat as 1 and so forth.

Label Encoding utilizing Python

  • Earlier than we proceed with label encoding in Python, allow us to import necessary information science libraries reminiscent of pandas and NumPy.
  • Then, with the assistance of panda, we’ll learn the Covid19_India information file which is in CSV format and test if the info file is loaded correctly. With the assistance of information(). We are able to discover {that a} state datatype is an object. Now we will proceed with LabelEncoding. 

Label Encoding could be carried out in 2 methods particularly:

  • LabelEncoder class utilizing scikit-learn library 
  • Class codes

Strategy 1 – scikit-learn library strategy

As Label Encoding in Python is a part of information preprocessing, therefore we’ll take an assist of preprocessing module from sklearn package deal and import LabelEncoder class as under:

After which:

  1. Create an occasion of LabelEncoder() and retailer it in labelencoder variable/object
  2. Apply match and remodel which does the trick to assign numerical worth to categorical worth and the identical is saved in new column known as “State_N”
  3. Word that we now have added a brand new column known as “State_N” which incorporates numerical worth related to categorical worth and nonetheless the column known as State is current within the dataframe. This column must be eliminated earlier than we feed the ultimate preprocess information to machine studying mannequin to study

Strategy 2 – Class Codes

  1. As you had already noticed that “State” column datatype is an object kind which is by default therefore, must convert “State” to a class kind with the assistance of pandas
  2. We are able to entry the codes of the classes by operating covid19[“State].cat.codes

One potential difficulty with label encoding is that more often than not, there is no such thing as a relationship of any sort between classes, whereas label encoding introduces a relationship. 

Within the above six lessons’ instance for “State” column, the connection seems as follows: 0 < 1 < 2 < 3 < 4 < 5. It signifies that numeric values could be misjudged by algorithms as having some form of order in them. This doesn't make a lot sense if the classes are, for instance, States. 

Additionally Learn: 5 widespread errors to keep away from whereas working with ML

There is no such thing as a such relation within the unique information with the precise State names, however, by utilizing numerical values as we did, a number-related connection between the encoded information could be made. To beat this drawback, we will use one-hot encoding as defined under.

One-Sizzling Encoding

On this strategy, for every class of a function, we create a brand new column (typically known as a dummy variable) with binary encoding (0 or 1) to indicate whether or not a specific row belongs to this class. 

Allow us to contemplate the earlier State column, and from the under picture, we will discover that new columns are created ranging from state identify Maharashtra until Uttar Pradesh, and there are 6 new columns created. 1 is assigned to a specific row that belongs to this class, and 0 is assigned to the remainder of the row that doesn’t belong to this class. 

A possible disadvantage of this methodology is a major improve within the dimensionality of the dataset (which known as a Curse of Dimensionality).

Which means, one-hot encoding is the truth that we’re creating further columns, one for every distinctive worth within the set of the explicit attribute we’d wish to encode. So, if we now have a categorical attribute that incorporates, say, 1000 distinctive values, that one-hot encoding will generate 1,000 further new attributes and this isn’t fascinating.

To maintain it easy, one-hot encoding is sort of a strong software, however it’s only relevant for categorical information which have a low variety of distinctive values.

Creating dummy variables introduces a type of redundancy to the dataset. If a function has three classes, we solely must have two dummy variables as a result of, if an commentary is neither of the 2, it should be the third one. That is also known as the dummy-variable lure, and it’s a finest apply to at all times take away one dummy variable column (referred to as the reference) from such an encoding.

Knowledge shouldn’t get into dummy variable traps that may result in an issue referred to as multicollinearity. Multicollinearity happens the place there’s a relationship between the impartial variables, and it’s a main menace to a number of linear regression and logistic regression issues.

To sum up, we should always keep away from label encoding in Python when it introduces false order to the info, which might, in flip, result in incorrect conclusions. Tree-based strategies (choice timber, Random Forest) can work with categorical information and label encoding. Nonetheless, for algorithms reminiscent of linear regression, fashions calculating distance metrics between options (k-means clustering, k-Nearest Neighbors) or Synthetic Neural Networks (ANN) are one-hot encoding.

One-Sizzling Encoding utilizing Python

Now, let’s see easy methods to apply one-hot encoding in Python. Getting again to our instance, in Python, this course of could be carried out utilizing 2 approaches as follows:

  • scikit-learn library 
  • Utilizing Pandas

Strategy 1 – scikit-learn library strategy

  1. As one-hot encoding can also be a part of information preprocessing, therefore we’ll take an assist of preprocessing module from sklearn package deal and them import OneHotEncoder class as under
  2. Instantiate the OneHotEncoder object, observe that parameter drop = ‘first’ will deal with dummy variable traps
  3. Carry out OneHotEncoding for categorical variable

4. Merge One Sizzling Encoded Dummy Variables to Precise information body however don’t forget to take away the precise column known as “State”
5. From the under output, we will observe, dummy variable lure has been taken care

Strategy 2 – Utilizing Pandas: with the assistance of get_dummies operate

  • As everyone knows, one-hot encoding is such a standard operation in analytics, that pandas present a operate to get the corresponding new options representing the explicit variable.
  • We’re contemplating the identical dataframe known as “covid19” and imported pandas library which is enough to carry out one sizzling encoding
  • As you discover under code, this generates a brand new DataFrame containing 5 indicator columns, as a result of as defined earlier for modeling we don’t want one indicator variable for every class; for a categorical function with Okay classes, we’d like solely Okay-1 indicator variables. In our instance, “State_Delhi” was eliminated
  • Within the case of 6 classes, we’d like solely 5 indicator variables to protect the data (and keep away from collinearity). That’s the reason the pd.get_dummies operate has one other Boolean argument, drop_first=True, which drops the primary class
  • For the reason that pd.get_dummies operate generates one other DataFrame, we have to concatenate (or add) the columns to our unique DataFrame and in addition don’t neglect to take away column known as “State”
  • Right here, we use the pd.concat operate, indicating with the axis=1 argument that we need to concatenate the columns of the two DataFrames given within the record (which is the primary argument of pd.concat). Don’t neglect to take away precise “State” column

Ordinal Encoding

An Ordinal Encoder is used to encode categorical options into an ordinal numerical worth (ordered set). This strategy transforms categorical worth into numerical worth in ordered units.

This encoding approach seems nearly just like Label Encoding. However, label encoding wouldn’t contemplate whether or not a variable is ordinal or not, however within the case of ordinal encoding, it should assign a sequence of numerical values as per the order of information.

Let’s create a pattern ordinal categorical information associated to the client suggestions survey, after which we’ll apply the Ordinal Encoder approach. On this case, let’s say the suggestions information is collected utilizing a Likert scale during which numerical code 1 is assigned to Poor, 2 for Good, 3 for Very Good, and 4 for Glorious. When you observe, we all know that 5 is healthier than 4, 5 is significantly better than 3, however taking the distinction between 5 and a pair of is meaningless (Glorious minus Good is meaningless).

Ordinal Encoding utilizing Python

With the assistance of Pandas, we’ll assign buyer survey information to a variable known as “Customer_Rating” via a dictionary after which we will map every row for the variable as per the dictionary.

That brings us to the tip of the weblog on Label Encoding in Python. We hope you loved this weblog. Additionally, try this free Python for Freshmen course to study the Fundamentals of Python. When you want to discover extra such programs and study new ideas, be a part of the Nice Studying Academy free course at this time.

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