Create a new column using the names of existing columns

Question

From a data frame in this structure

   1         2         3
0.2393876 0.3388785 0.4217339
0.2984463 0.3948705 0.3066832
0.3042033 0.3321453 0.3636514
0.2290906 0.2796392 0.4912702
0.1971198 0.3273682 0.4755120
0.2328518 0.3991225 0.3680256
0.3031909 0.3790213 0.3177878
0.2734835 0.3233044 0.4032121
0.3190916 0.3256503 0.3552581
0.2600000 0.3281130 0.4118871

How is it possible to compare the value in the three columns, find the highest and add the name of the column in a new variable. Example output:

1         2         3              highestcolumn
    0.2393876 0.3388785 0.4217339      3
    0.2984463 0.3948705 0.3066832      2
    0.3042033 0.3321453 0.3636514      3

Answer 1

Use which.max and apply on each row.

df$highestcolumn <- apply(df, 1, which.max)

> df
          X1        X2        X3 mean
1  0.2393876 0.3388785 0.4217339    3
2  0.2984463 0.3948705 0.3066832    2
3  0.3042033 0.3321453 0.3636514    3
4  0.2290906 0.2796392 0.4912702    3
5  0.1971198 0.3273682 0.4755120    3
6  0.2328518 0.3991225 0.3680256    2
7  0.3031909 0.3790213 0.3177878    2
8  0.2734835 0.3233044 0.4032121    3
9  0.3190916 0.3256503 0.3552581    3
10 0.2600000 0.3281130 0.4118871    3

Answer 2

We may use max.col

df$highestcolumn <- max.col(df, "first")

-output

> df
           1         2         3 highestcolumn
1  0.2393876 0.3388785 0.4217339             3
2  0.2984463 0.3948705 0.3066832             2
3  0.3042033 0.3321453 0.3636514             3
4  0.2290906 0.2796392 0.4912702             3
5  0.1971198 0.3273682 0.4755120             3
6  0.2328518 0.3991225 0.3680256             2
7  0.3031909 0.3790213 0.3177878             2
8  0.2734835 0.3233044 0.4032121             3
9  0.3190916 0.3256503 0.3552581             3
10 0.2600000 0.3281130 0.4118871             3