How to insert column in Julia DataFrame at a particular position

A DataFrame is a two-dimensional size-mutable tabular data structure similar to a table or spreadsheet. A DataFrame is mainly used for storing a set of related data values of various data types in tabular form with labeled rows and columns. Each row represents an observation or a data point. A column represents an observation's properties or attributes.

In Julia's ecosystem, the DataFrames.jl is a fast, powerful, flexible, and easy-to-use open-source data analysis and manipulation package. It provides numerous functions and methods for working with tabular data. This makes it a great general-purpose tool for data wrangling and analysis.

Column insertion in DataFrame

The addition of a new column to an existing DataFrame is a common data analysis operation. In this context, the method insertcols! of the DataFrames.jl package comes in handy when it is required to insert a column at a specific position or index.

Syntax

The syntax of the insertcol! method is the following:

insertcols!(df, col, (name=>val); after=false, 
makeunique=false, copycols=true)
Syntax

The main parameters of this function are listed below.

  • df: The DataFrame to be processed.

  • col: The position where we want to insert the new column.

  • name: The name of the column to add.

  • val: Either an AbstractVectorSupertype for one-dimensional arrays. including the contents of the new column or a value of any type other than AbstractArraySupertype for N-dimensional arrays which will be repeated to fill a new vector.

  • after: When true, the new columns are inserted after col.

  • makeunique: Specify the action to be taken if the new column name already exists in the DataFrame. When set to false, an error will be thrown otherwise a unique name will be allotted to the added column by appending 
    a suffix to it.

  • copycols: Specify whether vectors should be copied when they are passed as columns.

Let's go over the following examples showing how to insert a column in a Julia DataFrame at a particular position.

Code example 1

This example illustrates how to insert a new column containing values at a specific position in a DataFrame.

using DataFrames
df = DataFrame(
   id    =  [1,2,3]
  ,name   = ["Bassem","Celeste","Dominique"]
  ,salary = [3000,5000,4000]
)
print("The Dataframe before adding the new column:")
print(df)
arr = [45,35,28]
insertcols!(df, 3, :age => arr)
print("\n The Dataframe after adding the new column:")
print(df)

Code explanation

Let's examine the code widget above:

  • Lines 3–7: Create a simple DataFrame of 3 rows containing the employee's information.

  • Lines 9–10: Display a message and print out the created DataFrame.

  • Line 12: Define a vector containing the values of the column to add.

  • Line 13: Invoke the function insertcols! to create a new column named age at the third position (starting index = 1) while specifying as values for this newly added column the vector defined earlier.

  • Lines 15-16: Display a message and print out the processed DataFrame.

Code example 2

This example explores additional parameters of the function insertcols!

using DataFrames
df = DataFrame(
   id    =  [1,2,3]
  ,name   = ["Bassem","Celeste","Dominique"]
  ,salary = [3000,5000,4000]
)
print("The Dataframe before adding the new column:")
print(df)
rows = size(df)[1] 
insertcols!(df,1, :id => 1:rows, after=true, makeunique=true)
print("\n The Dataframe after adding the new column:")
print(df)

Code explanation

The code widget above looks like the one formerly explained except for:

  • Line 12: Get the number of rows of the DataFrame previously defined.

  • Line 13: Execute the function insertcols! while specifying as parameters:

    • df: The DataFrame is already defined.

    • 1: The index of the new column.

    • :id => 1:rows: The new column name and its respective content.

    • after=true: The new column will be added after the specified index (after the first column).

    • makeunique=true: Since the DataFrame already includes a column having the same name as the new column to be added id, therefore a new name will be automatically assigned to the new column.

Code example 3

This example demonstrates how to insert an empty column at a specific position in a DataFrame.

using DataFrames
df = DataFrame(
   id    =  [1,2,3]
  ,name   = ["Bassem","Celeste","Dominique"]
  ,salary = [3000,5000,4000]
)
print("The Dataframe before adding the new column:")
print(df)
insertcols!(df, 3, :age =>  missings(Int64))
print("\n The Dataframe after adding the new column:")
print(df)

Code explanation

The code widget above resembles the one previously elaborated except for:

  • Line 12: When calling the function insertcols! we specified as an argument missings(Int64) for the column age to be inserted. This means that the new column will be of type Int64 and initialized with the value missing.

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