Loop Append String creating too many additional DataFrame columns-CodePudding

Here is my code, I'm trying to change the column names after I subtract the values in one DataFrame from another, but it's just creating the incorrect column names.

colnames_in = ['One', 'Two', 'Three', 'Four', 'Five']

for i in range(len(colnames_in)):
    colnames_out = 'new col '   colnames_in[i]
    df[colnames_out[i]] = df_a[colnames_in[i]] - df_b[colnames_in[I]]

Instead of having "new col One", "new col Two" I'll just get "n", "e", "w" as the col names.

CodePudding user response：

You have at least two errors in your code sample. Both are in the final line. Here's a fixed version that should work.

colnames_in = ['One', 'Two', 'Three', 'Four', 'Five']

for i in range(len(colnames_in)):
    colnames_out = 'new col '   colnames_in[i]
    df[colnames_out] = df_a[colnames_in[i]] - df_b[colnames_in[i]]

If you want to make the for-loop a little more compact. Try this...

colnames_in = ['One', 'Two', 'Three', 'Four', 'Five']

for cname in colnames_in:
    colnames_out = 'new col '   cname
    df[colnames_out] = df_a[cname] - df_b[cname]

If you want to perform this process more "Pythonically", check out this previous SO question/answer.