first x characters of each element in numpy array

Question

I have a large dataset (6M rows). For a given column - timestamp I want to take the first 11 characters of each element and construct a new column. So far I am doing it using the apply method but it takes a long time.

df_value_dl['time_sec'] = df_value_dl.apply(lambda x: str(x['timestamp'])[0:10], axis=1)

While looking for faster methods I came across numpy arrays

What would be the correct syntax to do this using np arrays. Thanks

Answer 1

Just in case you haven't found an solution yet: This

df_value_dl['time_sec'] = df_value_dl['timestamp'].astype('string').str[:10]

should be faster than apply .