How to check if an element is an empty list in pandas?

Question

One of the column in my df stores a list, and some of the raws have empty items in the list. For example:

[]

["X", "Y"]

[]

etc...

How can only take the raw whose list is not empty?

The following code does not work.

df[df["col"] != []] # ValueError: Lengths must match to compare

df[pd.notnull(df["col"])] # The code doesn't issue an error but the result includes an empty list

df[len(df["col"]) != 0] # KeyError: True

Answer 1

You can do it like this:

df[df["col"].str.len() != 0]

Answer 2

To extract all the data from a column containing an empty list, you can filter out rows in DataFrame by using lambda function.

import pandas as pd

sample_data={

‘col’:[ [ ], [ “X”, “Y”], [ ], [“Z] ]

}

df=pd.DataFrame(sample_data)

filtered_data= df[ df[‘col’ ].apply(lambda x: len(x)>0) ]

print(filtered_data)

This will filter out the empty list and output will be: 

    col

1 [X,Y]

3 [Z]

Answer 3

You are trying to filter rows in your DataFrame in the columns where the values are an empty list([]). To perform this operation you can use lambda function to retrieve all values in the specific column and need to check if the length of the list is greater than 0.

Code:

import pandas as pd

d = {“column_1”: [[], [‘x’, ‘y’], [], [‘A’], [2,3]]}

df = pd.DataFrame(d)

filtered_df = df[df["column_1"].apply(lambda x: len(x) > 0)]

print(filtered_df)

Output:

      Column1

1     [‘x’,’y’]

3     [‘A’]

4     [2,3]