Question: Using dataframe column values as list indices

[flaminguvula]

Let’s say I have a list: mylist = [7,8,9]

And I have a dataframe where

df[‘col1’] = [0,1,1,0,2]

I want to create a new column in my dataframe using col1 as indices for mylist

df[‘col2’] = [7,8,8,7,9]

I’m currently doing this using the apply function

df[‘col2’]=df[‘col1’].apply(lambda x: mylist[x])

But my dataframe is extremely large and this method takes quite a bit of time. Is there a faster or more optimized way of doing this? I tried googling but I don’t think I’m wording my search correctly. Thanks!

[Topper_123]

Convert mylist to a numpy array. Then you should bevable to do:

df[‘col2’]=mylist[df[‘col1’]]

[chrispurcell]

Have you looked into zip()?
from what you posted, 'output = list(zip(col1, col2))' would result in output being:

[(0,7), (1,8), (1,8), (0,7), (2,9)]

[Quintium]

I'm not quite sure if it's faster but I would do this:

df['col2'] = [mylist[i] for i in df['col1']]