Set value for particular cell in pandas DataFrame using index

Question

I\'ve created a Pandas DataFrame

df = DataFrame(index=[\'A\',\'B\',\'C\'], columns=[\'x\',\'y\'])

and got this

    x    y
A  NaN         


        

Answer 1

One way to use index with condition is first get the index of all the rows that satisfy your condition and then simply use those row indexes in a multiple of ways

conditional_index = df.loc[ df['col name']  ].index

Example condition is like

==5, >10 , =="Any string", >= DateTime

Then you can use these row indexes in variety of ways like

1. Replace value of one column for conditional_index

df.loc[conditional_index , [col name]]= 

2. Replace value of multiple column for conditional_index

df.loc[conditional_index, [col1,col2]]= 

3. One benefit with saving the conditional_index is that you can assign value of one column to another column with same row index

df.loc[conditional_index, [col1,col2]]= df.loc[conditional_index,'col name']

This is all possible because .index returns a array of index which .loc can use with direct addressing so it avoids traversals again and again.