How do I insert elements systematically within a vector in R?

Question

I have the vector y=[-2 -4 -6 ... -1000], and I want to insert a 0 before every element to change the vector into: y=[0 -2 0 -4 0 -6 ... 0 -1000].

How do I do this? Should I try to directly insert elements into vector y or create a separate vector z with just 0's and try to merge the 2?

Also, is there a way to do this without using loops or index vectors?

score 5 · Accepted Answer · answered Oct 14 '13 at 06:28

5

You could use rbind as follows:

y <- seq(from=2, to=10, by=2)*-1
y
# [1]  -2  -4  -6  -8 -10
as.vector(rbind(0, y))
# [1]   0  -2   0  -4   0  -6   0  -8   0 -10

answered Oct 14 '13 at 06:28

Thank you! A quick question: Could I use the same "rbind" function to add several 0's before each element in y? – Jess Oct 14 '13 at 06:42
@Jess, did you try it ;) --- `as.vector(rbind(0, 0, y))` seems to add two zeroes before each element for me. – A5C1D2H2I1M1N2O1R2T1 Oct 14 '13 at 06:45
Ahh I overthought it. I tried it by adding an actual vector of 0's in the function, which doesn't work. – Jess Oct 14 '13 at 06:50
For general interleaving, this answer has a cool approach: http://stackoverflow.com/a/16443987/1191259 – Frank Oct 14 '13 at 06:52
@Jess, No problem. You were just tripped up by recycling, then. – A5C1D2H2I1M1N2O1R2T1 Oct 14 '13 at 07:07

1 Answers1