Using If/Else on a data frame

Question

I have a data set which looks something like

data<-c(0,1,2,3,4,2,3,1,4,3,2,4,0,1,2,0,2,1,2,0,4)
frame<-as.data.frame(data)

I now want to create a new variable within this data frame. If the column "data" reports a number of 2 or more, I want it to have "2" in that row, and if there is a 1 or 0 (e.g. the first two observations), I want the new variable to have a "1" for that observation.

I am trying to do this using the following code:

frame$twohouses<- if (any(frame$data>=2)) {frame$twohouses=2} else {frame$twohouses=1}

However if I run these 3 lines of script, every observation in the column "twohouses" is coded with a 2. However a number of them should be coded with a 1.

So my question: what am I doing wrong with my if else line or script? Or is there an alternative way to do this.

My question is similar to this one: Using ifelse on factor in R

ut no one has answered that question.

You need to use the function `ifelse`, not `if`. – Andrie Aug 08 '12 at 13:09 — Andrie, Aug 08 '12 at 13:09

score 68 · Accepted Answer · answered Aug 08 '12 at 13:11

68

Use ifelse:

frame$twohouses <- ifelse(frame$data>=2, 2, 1)
frame
   data twohouses
1     0         1
2     1         1
3     2         2
4     3         2
5     4         2
...
16    0         1
17    2         2
18    1         1
19    2         2
20    0         1
21    4         2

The difference between if and ifelse:

if is a control flow statement, taking a single logical value as an argument
ifelse is a vectorised function, taking vectors as all its arguments.

The help page for if, accessible via ?"if" will also point you to ?ifelse

answered Aug 08 '12 at 13:11

Andrie

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naturally it would turn out to be something frustratingly easy after spending ages fighting with R. Thanks! – Timothy Alston Aug 08 '12 at 13:14
@TimothyAlston I added some pointers on how to get help on `if` and `ifelse` – Andrie Aug 08 '12 at 13:19
Thanks for this. This worked well for a larger data problem that I was working on and ended up being more efficient than many of the other methods I was attempting. Simple, but compelling. – Nathaniel Payne May 06 '14 at 08:23

score 3 · Answer 2 · answered Aug 08 '12 at 13:11

Try this

frame$twohouses <- ifelse(frame$data>1, 2, 1)
 frame
   data twohouses
1     0         1
2     1         1
3     2         2
4     3         2
5     4         2
6     2         2
7     3         2
8     1         1
9     4         2
10    3         2
11    2         2
12    4         2
13    0         1
14    1         1
15    2         2
16    0         1
17    2         2
18    1         1
19    2         2
20    0         1
21    4         2

Using If/Else on a data frame

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