Select the highest value of a column set of a df and take the column name of that highest value in R

Question

Guys I have a table in the R in which I wanted to look for the highest value in a given set of columns and given this higher value, return in a new column the name of the column in which that higher value was.

For example, given the df below I wanted to look for the highest value of each row between columns of A to F and create a new column called colunaOriginal containing the name of the column in which the largest was.

For the first row the highest value would be 100 (in column A) and the information colunaA would be in the column colunaOriginal.

df_maior_valor <- 
structure(list(A = c(100, 49, 30, 11, 7, 0, 1, 5, 7, 12), B = c(50, 
51, 20, 10, 3, 10, 2, 6, 3, 3), C = c(0, 1, 5, 2, 5, 0, 0, 2, 
1, 1), D = c(0, 0, 1, 0, 1, 0, 0, 0, 3, 2), E = c(0, 0, 0, 0, 
1, 0, 0, 0, 1, 0), F = c(0, 0, 0, 0, 1, 0, 0, 0, 0, 0)), .Names = c("A", 
"B", "C", "D", "E", "F"), row.names = c(NA, 10L), class = "data.frame")

Answer 1

Without using any extra packages, I would solve it as follows. First, I find out which column has the highest value. This response is given by the position of the column:

x <- apply(df_maior_valor, 1, which.max)
x
 1  2  3  4  5  6  7  8  9 10 
 1  2  1  1  1  2  2  2  1  1

Then I turn x in a factor.

x <- as.factor(x)

This factor will have numerical levels. Therefore, I need to name this levels as defined in the original problem:

levels(x) <- paste0("coluna", LETTERS[1:6])

x
      1       2       3       4       5       6       7       8       9      10 
colunaA colunaB colunaA colunaA colunaA colunaB colunaB colunaB colunaA colunaA 
Levels: colunaA colunaB colunaC colunaD colunaE colunaF

Next, I organize everything into a new data frame:

data.frame(df_maior_valor, colunaOriginal=x)
     A  B C D E F colunaOriginal
1  100 50 0 0 0 0        colunaA
2   49 51 1 0 0 0        colunaB
3   30 20 5 1 0 0        colunaA
4   11 10 2 0 0 0        colunaA
5    7  3 5 1 1 1        colunaA
6    0 10 0 0 0 0        colunaB
7    1  2 0 0 0 0        colunaB
8    5  6 2 0 0 0        colunaB
9    7  3 1 3 1 0        colunaA
10  12  3 1 2 0 0        colunaA