How to get a column in python

How to get or print Pandas DataFrame Column Names? You can get the Pandas DataFrame Column Names by using DataFrame.columns.values method and to get it as a list use tolist(). Each column in a Pandas DataFrame has a label/name that specifies what type of value it holds/represents. Getting a column names is useful when you wanted to access all columns by name programmatically or manipulate the values of all columns. In this article, I will explain different ways to get column names from pandas DataFrame headers with examples.

To get a list of columns from the DataFrame header use DataFrame.columns.values.tolist() method. Below is an explanation of each section of the statement.

• .columns returns an Index object with column names. This preserves the order of column names.
• .columns.values returns an array and this has a helper function .tolist() that returns a list of column names.

1. Quick Examples of Get Column Names

Following are some quick examples of how to get column names from pandas DataFrame, If you wanted to print it to console just use the print() statment.

# Below are some quick examples

# Get the list of all column names from headers
column_names = list(df.columns.values)

# Get the list of all column names from headers
column_names = df.columns.values.tolist()

#Using list(df) to get the column headers as a list
column_names = list(df.columns)

#Using list(df) to get the list of all Column Names
column_names = list(df)

# Dataframe show all columns sorted list
column_names=sorted(df)

# Get all Column Header Labels as List
for column_headers in df.columns: 
    print(column_headers)
    
column_names = df.keys().values.tolist()

# Get all numeric columns
numeric_columns = df._get_numeric_data().columns.values.tolist()

# Simple Pandas Numeric Columns Code
numeric_columns=df.dtypes[df.dtypes == "int64"].index.values.tolist()

Create a Pandas DataFrame from Dict with a few rows and with columns names Courses, Fee, Duration and Discount.

import pandas as pd
import numpy as np

technologies= {
    'Courses':["Spark","PySpark","Hadoop","Python","Pandas"],
    'Fee' :[22000,25000,23000,24000,26000],
    'Duration':['30days','50days','30days', None,np.nan],
    'Discount':[1000,2300,1000,1200,2500]
          }
df = pd.DataFrame(technologies)
print(df)

You can get the column names from pandas DataFrame using df.columns.values, and pass this to python list() function to get it as list, once you have the data you can print it using print() statement. I will take a moment to explain what is happening on this statement, df.columns attribute returns an Index object which is a basic object that stores axis labels. Index object provides a property Index.values that returns data in an array, in our case it returns column names in an array.

Note that df.columns preserve the order of the columns as-is.

To convert an array of column names into a list, we can use either .toList() on array object or use list(array object).

# Get the list of all column names from headers
column_headers = list(df.columns.values)
print("The Column Header :", column_headers)

Yields below output.

The Column Header : ['Courses', 'Fee', 'Duration', 'Discount']

You can also use df.columns.values.tolist() to get the DataFrame column names.

# Get the list of all column names from headers
column_headers = df.columns.values.tolist()
print("The Column Header :", column_headers)

3. Use list(df) to Get Column Names from DataFrame

Use list(df) to get the column header from pandas DataFrame. You can also use list(df.columns) to get column names.

#Using list(df) to get the column headers as a list
column_headers = list(df.columns)

#Using list(df) to get the list of all Column Names
column_headers = list(df)

4. Get Column Names in Sorting order

In order to get a list of column names in a sorted order use sorted(df) function. this function returns column names in alphabetical order.

# Dataframe show all columns sorted list
col_headers=sorted(df)
print(col_headers)

Yields below output. Notice the difference of output from above.

['Courses', 'Discount', 'Duration', 'Fee']

5. Access All Column Names by Iterating

Sometimes you may need to iterate over all columns and apply some function, you can do this as below.

# Get all Column Header Labels as List
for column_headers in df.columns: 
    print(column_headers)

Yields below output.

Courses
Fee
Duration
Discount

6. Get Column Headers Using the keys() Method

df.keys() is another approach to get all column names as a list from pandas DataFrame.

column_headers = df.keys().values.tolist()
print("The Column Header :", column_headers)

Yields below output.

The Column Header : Index(['Courses', 'Fee', 'Duration', 'Discount'], dtype='object')

7. Get All Numeric Column Names

Sometimes while working on the analytics, you may need to work only on numeric columns, hence you would be required to get all columns of a specific data type. For example, getting all columns of numeric data type can get using undocumented function df._get_numeric_data().

# Get all numeric columns
numeric_columns = df._get_numeric_data().columns.values.tolist()
print(numeric_columns)

Yields below output.

['Fee', 'Discount']

Use for df.dtypes[df.dtypes!="Courses"].index: This is another simple code for finding numeric columns in a pandas DataFrame.

# Simple Pandas Numeric Columns Code
numeric_columns=df.dtypes[df.dtypes == "int64"].index.values.tolist()

Yields same output as above.

9. Complete Example of pandas Get Columns Names

import pandas as pd
import numpy as np

technologies= {
    'Courses':["Spark","PySpark","Hadoop","Python","Pandas"],
    'Fee' :[22000,25000,23000,24000,26000],
    'Duration':['30days','50days','30days', None,np.nan],
    'Discount':[1000,2300,1000,1200,2500]
          }
df = pd.DataFrame(technologies)
print(df)

# Get the list of all column names from headers
column_headers = list(df.columns.values)
print("The Column Header :", column_headers)

# Get the list of all column names from headers
column_headers = df.columns.values.tolist()
print("The Column Header :", column_headers)

#Using list(df) to get the column headers as a list
column_headers = list(df.columns)

#Using list(df) to get the list of all Column Names
column_headers = list(df)

# Dataframe show all columns sorted list
col_headers=sorted(df)
print(col_headers)

# Get all Column Header Labels as List
for column_headers in df.columns: 
    print(column_headers)
    
column_headers = df.keys().values.tolist()
print("The Column Header :", column_headers)

# Get all numeric columns
numeric_columns = df._get_numeric_data().columns.values.tolist()
print(numeric_columns)

# Simple Pandas Numeric Columns Code
numeric_columns=df.dtypes[df.dtypes == "int64"].index.values.tolist()
print(numeric_columns)

Conclusion

In this article, you have learned how to get or print the column names using df.columns, list(df), df.keys, and also learned how to get all column names of type integer, finally getting column names in a sorted order e.t.c

Happy Learning !!

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• How to Combine Two Columns of Text in Pandas DataFrame
• What is a Pandas DataFrame Explained With Examples

References

• https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.head.html

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