Change Pandas DataFrame column values from array to first value in array

Question

I have a DataFrame with a labels column. The labels column is currently an array, and I would like to map the entire column to the first item of the array for each row without naively iterating.

For example, if I have 2 rows with labels values ['1','m'], ['0'], I would like to map the current values to the new values '1','0'.

Answer 1

You can use .str for this:

df['labels'] = df['labels'].str[0]

However, it (and other possible ways) is essentially just a loop:

df['labels'] = [x[0] for x in df['labels'] ]

I'd recommend doing a loop since you have better control of error handling, eg:

# this handles empty array as well as NaN values
df['labels'] = [x[0] if x else np.nan for x in df['labels']]