Create a new column with letters following the number of rows

Question

I would like to create a new column with letters, following the number of rows in the data frame.

Data:

set.seed(42)
df = data.frame(matrix(rnorm(20), nrow=10))
df
            X1         X2
1   1.37095845  1.3048697
2  -0.56469817  2.2866454
3   0.36312841 -1.3888607
4   0.63286260 -0.2787888
5   0.40426832 -0.1333213
6  -0.10612452  0.6359504
7   1.51152200 -0.2842529
8  -0.09465904 -2.6564554
9   2.01842371 -2.4404669
10 -0.06271410  1.3201133

I could insert letters by setting the number of rows manually. I would like to do set it accordingly to the number of rows in the data frame.

df$label = as.character(LETTERS[1:10])
df
            X1         X2 label
1   1.37095845  1.3048697     A
2  -0.56469817  2.2866454     B
3   0.36312841 -1.3888607     C
4   0.63286260 -0.2787888     D
5   0.40426832 -0.1333213     E
6  -0.10612452  0.6359504     F
7   1.51152200 -0.2842529     G
8  -0.09465904 -2.6564554     H
9   2.01842371 -2.4404669     I
10 -0.06271410  1.3201133     J

Answer 1

You can use seq_len with nrow, but works only up to 26 rows.

df$label <-  LETTERS[seq_len(nrow(df))]

In case you have more rows and want to repeat LETTEERS:

df$label <- LETTERS[1 + seq(0, length.out = nrow(df)) %% 26]