How do i select a column in a list python?

Question

Use DataFrame.loc[] and DataFrame.iloc[] to select a single column or multiple columns from pandas DataFrame by column names/label or index position respectively. where loc[] is used with column labels/names and iloc[] is used with column index/position. You can also use these operators to select rows from pandas DataFrame. Also, refer to a related article how to get cell value from pandas DataFrame.

Table of Contents Show

1. Quick Examples of Select Columns from Pandas DataFrame
2. Using loc[] to Select Columns by Name
2.1 Select DataFrame Columns by Name
2.2 Select Multiple Columns
2.3 Select DataFrame Columns by Range
2.4 Select Every Alternate Column
3. Pandas iloc[] to Select Column by Index or Position
3.1. Select Multiple Columns by Index Position
3.2 Select Columns by Position Range
4. Complete Example of pandas Select Columns
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How do I select a column in pandas Python?

Pandas DataFrame is a two-dimensional tabular data structure with labeled axes. i.e. columns and rows. Selecting columns from DataFrame results in a new DataFrame containing only specified selected columns from the original DataFrame.

In this article, I will explain how to select single or multiple columns from DataFrame by column labels & index, certain positions of the column, and by range e.t.c with examples.

1. Quick Examples of Select Columns from Pandas DataFrame

If you are in a hurry, below are some quick examples of how to select single or multiple columns from pandas DataFrame by column name and index.


# Below are quick example

# By using df[] Notation
df2 = df[["Courses","Fee","Duration"]] # select multile columns

# Using loc[] to take column slices
df2 = df.loc[:, ["Courses","Fee","Duration"]] # Selecte multiple columns
df2 = df.loc[:, ["Courses","Fee","Discount"]] # Select Random columns
df2 = df.loc[:,'Fee':'Discount'] # Select columns between two columns
df2 = df.loc[:,'Duration':]  # Select columns by range
df2 = df.loc[:,:'Duration']  # Select columns by range
df2 = df.loc[:,::2]          # Select every alternate column

# Using iloc[] to select column by Index
df2 = df.iloc[:,[1,3,4]] # Select columns by Index
df2 = df.iloc[:,1:4] # Select between indexes 1 and 4 (2,3,4)
df2 = df.iloc[:,2:] # Select From 3rd to end
df2 = df.iloc[:,:2] # Select First Two Columns

Now, let’s create a DataFrame with a few rows and columns and execute some examples of how to select columns in pandas. Our DataFrame contains column names Courses, Fee, Duration, and Discount.


import pandas as pd
technologies = {
    'Courses':["Spark","PySpark"],
    'Fee' :[20000,25000],
    'Duration':['30days','40days'],
    'Discount':[1000,2300]
              }
df = pd.DataFrame(technologies)
print(df)

Yields below output.


   Courses    Fee Duration  Discount   Tutor
0    Spark  20000   30days      1000  Michel
1  PySpark  25000   40days      2300     Sam

2. Using loc[] to Select Columns by Name

By using pandas.DataFrame.loc[] you can select columns by names or labels. To select the columns by names, the syntax is df.loc[:,start:stop:step]; where start is the name of the first column to take, stop is the name of the last column to take, and step as the number of indices to advance after each extraction; for example, you can select alternate columns. Or, use the syntax: [:,[labels]] with labels as a list of column names to take.


#loc[] syntax to slice columns
df.loc[:,start:stop:step]

2.1 Select DataFrame Columns by Name

To select single or multiple columns by labels or names, all you need is to provide the names of the columns as a list. Here we use the [] notation instead of df.loc[,start:stop:step] approach.


# Select Columns by labels
df2 = df[["Courses","Fee","Duration"]]
#Returns
#   Courses    Fee Duration
#0    Spark  20000   30days
#1  PySpark  25000   40days

2.2 Select Multiple Columns

Sometimes you may want to select multiple columns from pandas DataFrame, you can do this by passing multiple column names/labels as a list. Note that loc[] also supports multiple conditions when selecting rows based on column values.


# Select Multiple Columns
df2 = df.loc[:, ["Courses","Fee","Discount"]]
#Returns
#   Courses    Fee  Discount
#0    Spark  20000      1000
#1  PySpark  25000      2300

2.3 Select DataFrame Columns by Range

When you wanted to select columns by the range, provide start and stop column names.

By not providing a start column, loc[] selects from the beginning.
By not providing stop, loc[] selects all columns from the start label.
Providing both start and stop, selects all columns in between.


# Select all columns between Fee an Discount columns
df2 = df.loc[:,'Fee':'Discount']
#Returns
#     Fee Duration  Discount
#0  20000   30days      1000
#1  25000   40days      2300

# Select from 'Duration' column
df2 = df.loc[:,'Duration':]
#Returns
#  Duration  Discount   Tutor
#0   30days      1000  Michel
#1   40days      2300     Sam

# Select from beginning and end at 'Duration' column
df2 = df.loc[:,:'Duration']
#Returns
#   Courses    Fee Duration
#0    Spark  20000   30days
#1  PySpark  25000   40days

2.4 Select Every Alternate Column

Using loc[], you can also select every other column from pandas DataFrame.


# Select every alternate column
df2 = df.loc[:,::2]
#Returns
#   Courses Duration   Tutor
#0    Spark   30days  Michel
#1  PySpark   40days     Sam

3. Pandas iloc[] to Select Column by Index or Position

By using pandas.DataFrame.iloc[] you can select columns from DataFrame by position/index. ; Remember index starts from 0. You can use iloc[] with the syntax [:,start:stop:step] where start indicates the index of the first column to take, stop indicates the index of the last column to take, and step indicates the number of indices to advance after each extraction. Or, use the syntax: [:,[indices]] with indices as a list of column indices to take.

3.1. Select Multiple Columns by Index Position

Below example retrieves "Fee","Discount" and "Duration" and returns a new DataFrame with the columns selected.


# Selected by column position
df2 = df.iloc[:,[1,3,4]]
#Returns
#     Fee  Discount   Tutor
#0  20000      1000  Michel
#1  25000      2300     Sam

3.2 Select Columns by Position Range

You can also slice a DataFrame by a range of positions.


# Select between indexes 1 and 4 (2,3,4)
df2 = df.iloc[:,1:4]
#Returns
#     Fee Duration  Discount
#0  20000   30days      1000
#1  25000   40days      2300

# Select From 3rd to end
df2 = df.iloc[:,2:]
#Returns
#  Duration  Discount   Tutor
#0   30days      1000  Michel
#1   40days      2300     Sam

# Select First Two Columns
df2 = df.iloc[:,:2]
#Returns
#   Courses    Fee
#0    Spark  20000
#1  PySpark  25000

To get the last column use df.iloc[:,-1:] and to get just first column df.iloc[:,:1]

4. Complete Example of pandas Select Columns

Below is a complete example of how to select columns from pandas DataFrame.


import pandas as pd
technologies = {
    'Courses':["Spark","PySpark"],
    'Fee' :[20000,25000],
    'Duration':['30days','40days'],
    'Discount':[1000,2300],
    'Tutor':['Michel','Sam']
              }
df = pd.DataFrame(technologies)
print(df)

# Select multiple columns
print(df[["Courses","Fee","Duration"]])

# Select Random columns
print(df.loc[:, ["Courses","Fee","Discount"]])

# Select columns by range
print(df.loc[:,'Fee':'Discount']) 
print(df.loc[:,'Duration':])
print(df.loc[:,:'Duration'])

# Select every alternate column
print(df.loc[:,::2])

# Selected by column position
print(df.iloc[:,[1,3,4]])

# Select between indexes 1 and 4 (2,3,4)
print(df.iloc[:,1:4])

# Select From 3rd to end
print(df.iloc[:,2:])

# Select First Two Columns
print(df.iloc[:,:2])

Conclusion

In this article, you have learned how to select single or multiple columns from pandas DataFrame using DataFrame.loc[], and DataFrame.iloc[] properties. To understand the similarities and differences of these two refer to pandas loc vs iloc.

Happy Learning !!

References

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

How do I select a column in a list in Python?

This is the most basic way to select a single column from a dataframe, just put the string name of the column in brackets. Returns a pandas series. Passing a list in the brackets lets you select multiple columns at the same time.