Finding list of index corresponding to list of element of a dataframe in Python

Question

I have a dataframe with millions of lines. I need to get the corresponding indexes of hundreds of thousands of elements that are present in the original dataframe.

I currently use this code:

df[df['processed_col'] == element.index[0]

to find the position of 'element' into the whole dataframe.

Instead of doing a loop which is very long, is there a way to take a list like element1, element2,..., elementN as input, which would return a list of corresponding indices:

df[df['processed_col'] == [element1, element2, ..., elementN].index[0]

Hmmm, you need df[df['processed_col'].isin([element1, element2,..., elementN])].index[0] — jezrael
– jezrael, Commented Aug 24, 2016 at 10:25
Sorry your question is unclear are you asking for df[df['processed_col'].isin(some_list)].index? — EdChum
– EdChum, Commented Aug 24, 2016 at 10:26
@jezrael I think the OP wants the index values where the values exist, index[0] will return the first index value — EdChum
– EdChum, Commented Aug 24, 2016 at 10:27
Yes, if need only first value, use index[0], if need all values, use index... — jezrael
– jezrael, Commented Aug 24, 2016 at 10:28

jezrael · Accepted Answer · 2016-08-24 12:30:35Z

3

IIUC you need isin if find first value of index:

df[df['processed_col'].isin([element1, element2,..., elementN])].index[0]

or if want all values of index, remove [0] only:

df[df['processed_col'].isin([element1, element2,..., elementN])].index

If need convert to list use tolist:

df[df['processed_col'].isin([element1, element2,..., elementN])].index.tolist()

edited Aug 24, 2016 at 12:30

answered Aug 24, 2016 at 10:30

jezrael

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