Repeat vector to fill down column in data frame

Question

Seems like this very simple maneuver used to work for me, and now it simply doesn\'t. A dummy version of the problem:

df <- data.frame(x = 1:5) # create simpl         


        

Answer 1

If the total number of rows is a multiple of the length of your new vector, it works fine. When it is not, it does not work everywhere. In particular, probably you have used this type of recycling with matrices:

data.frame(1:6, 1:3, 1:4) # not a multiply
# Error in data.frame(1:6, 1:3, 1:4) : 
#   arguments imply differing number of rows: 6, 3, 4
data.frame(1:6, 1:3) # a multiple
#   X1.6 X1.3
# 1    1    1
# 2    2    2
# 3    3    3
# 4    4    1
# 5    5    2
# 6    6    3
cbind(1:6, 1:3, 1:4) # works even with not a multiple
#      [,1] [,2] [,3]
# [1,]    1    1    1
# [2,]    2    2    2
# [3,]    3    3    3
# [4,]    4    1    4
# [5,]    5    2    1
# [6,]    6    3    2
# Warning message:
# In cbind(1:6, 1:3, 1:4) :
#   number of rows of result is not a multiple of vector length (arg 3)

Answer 2

If the vector can be evenly recycled, into the data.frame, you do not get and error or a warning:

df <- data.frame(x = 1:10)
df$z <- 1:5

This may be what you were experiencing before.

You can get your vector to fit as you mention with rep_len:

df$y <- rep_len(1:3, length.out=10)

This results in

df
    x z y
1   1 1 1
2   2 2 2
3   3 3 3
4   4 4 1
5   5 5 2
6   6 1 3
7   7 2 1
8   8 3 2
9   9 4 3
10 10 5 1

Note that in place of rep_len, you could use the more common rep function:

df$y <- rep(1:3,len=10)

From the help file for rep:

rep.int and rep_len are faster simplified versions for two common cases. They are not generic.