[R] Extracting part of a factor

[Sarah Goslee]

As everyone has been telling you, as.factor().
If you like the mutate approach, you can call as.factor(test$subject)
to convert it.

Here's a one-liner with reproducible data.


testdata <- structure(list(subject = structure(1:6, .Label = c("001-002",
"002-003", "003-004", "004-005", "005-006", "006-007"), class = "factor"),
    group = structure(c(1L, 1L, 1L, 2L, 2L, 2L), .Label = c("boys",
    "girls"), class = "factor"), wk1 = c(2L, 7L, 9L, 5L, 2L,
    1L), wk2 = c(3L, 6L, 4L, 7L, 6L, 4L), wk3 = c(4L, 5L, 6L,
    8L, 3L, 7L), wk4 = c(5L, 4L, 1L, 9L, 8L, 4L)), .Names = c("subject",
"group", "wk1", "wk2", "wk3", "wk4"), class = "data.frame", row.names = c(NA,
-6L))

testdata$subject <- as.factor(substring(as.character(testdata$subject), 1, 3))

> testdata
  subject group wk1 wk2 wk3 wk4
1     001  boys   2   3   4   5
2     002  boys   7   6   5   4
3     003  boys   9   4   6   1
4     004 girls   5   7   8   9
5     005 girls   2   6   3   8
6     006 girls   1   4   7   4
> str(testdata)
'data.frame': 6 obs. of  6 variables:
 $ subject: Factor w/ 6 levels "001","002","003",..: 1 2 3 4 5 6
 $ group  : Factor w/ 2 levels "boys","girls": 1 1 1 2 2 2
 $ wk1    : int  2 7 9 5 2 1
 $ wk2    : int  3 6 4 7 6 4
 $ wk3    : int  4 5 6 8 3 7
 $ wk4    : int  5 4 1 9 8 4

Sarah

On Fri, Mar 4, 2016 at 1:00 PM, KMNanus <kmnanus at gmail.com> wrote:
>
> Here’s the dataset I’m working with, called test -
>
> subject group wk1 wk2 wk3 wk4 place
> 001-002 boys 2 3 4 5
> 002-003 boys 7 6 5 4
> 003-004 boys 9 4 6 1
> 004-005 girls 5 7 8 9
> 005-006 girls 2 6 3 8
> 006-007 girls 1 4 7 4
>
>
> if I call mutate(test, place = substr(subject,1,3), “001 is the first observation in the place column
>
> But it’s a character and “subject” is a factor.  I need place to be a factor, too, but I need the observations to be ONLY the first three numbers of “subject.”
>
> Does that make my request more understandable?