conditionally replacing values in a column-CodePudding

I have a pandas dataframe, where the 2nd, 3rd and 6th columns look like so:

start	end	strand
108286	108361
734546	734621	-
761233	761309

I'm trying to implement a conditional where, if strand is , then the value in end becomes the equivalent value in start 1, and if strand is -, then the value in start becomes the value in end, so the output should look like this:

start	end	strand
108286	108287
734620	734621	-
761233	761234

And where the pseudocode may look like this:

if df["strand"] == " ": 
        df["end"] = df["start"]   1
        
else:
        df["start"] = df["end"] - 1

I imagine this might be best done with loc/iloc or numpy.where? but I can't seem to get it to work, as always, any help is appreciated!

CodePudding user response：

You are correct, loc is the operator you are looking for

df.loc[df.strand==' ','end'] = df.loc[df.strand==' ','start'] 1
df.loc[df.strand=='-','start'] = df.loc[df.strand=='-','end']-1

CodePudding user response：

You could also use numpy.where:

import numpy as np
df[['start', 'end']] = np.where(df[['strand']]=='-', df[['end','end']]-[1,0], df[['start','start']] [0,1])

Note that this assumes strand can have one of two values: or -. If it can have any other values, we can use numpy.select instead.

Output:

    start     end strand
0  108286  108287       
1  734620  734621      -
2  761233  761234