How to create component data frames (subsets) in R based on column values?

Question

I would like to split a data frame into several component frames based on values ​​in one column. In my example, I want to split dat into dat.1, dat.2 and dat.3 using the values ​​in the "cond" column. Is there a simple team that could achieve this?

dat sub cond trial time01 time02 1 1 1 2774 8845 1 1 2 2697 9945 1 2 1 2219 9291 1 2 2 3886 7890 1 3 1 4011 9032 2 2 1 3478 8827 2 2 2 2263 8321 2 3 1 4312 7576 3 1 1 4219 7891 3 3 1 3992 6674 dat.1 sub cond trial time01 time02 1 1 1 2774 8845 1 1 2 2697 9945 3 1 1 4219 7891 dat.2 sub cond trial time01 time02 2 2 1 3478 8827 2 2 2 2263 8321 1 2 1 2219 9291 1 2 2 3886 7890 dat.3 sub cond trial time01 time02 1 3 1 4011 9032 2 3 1 4312 7576 3 3 1 3992 6674 

Perhaps because I'm a newbie to R, I still haven't figured out how to do this, despite browsing and searching for solutions suggested in several similar forums. Thank you in advance for any answers.

A dput() data:

 structure(list(sub = c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 3L, 3L ), cond = c(1L, 1L, 2L, 2L, 3L, 2L, 2L, 3L, 1L, 3L), trial = c(1L, 2L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L), time01 = c(2774L, 2697L, 2219L, 3886L, 4011L, 3478L, 2263L, 4312L, 4219L, 3992L), time02 = c(8845L, 9945L, 9291L, 7890L, 9032L, 8827L, 8321L, 7576L, 7891L, 6674L )), .Names = c("sub", "cond", "trial", "time01", "time02"), class = "data.frame", row.names = c(NA, -10L)) 

Answer 1

I think the easiest way is through split :

 split(dat, dat$cond) 

Note that this split returns a list of data.frames.

To get single frames of data from a list, you can use a loop like this to make individual objects (implicit in a lapply ):

 tmp <- split(dat, dat$cond) lapply(1:length(tmp), function(x) assign(paste("dat.", x, sep = ""), tmp[[x]], envir = .GlobalEnv)) 

However, using a list is probably larger than R ish and will be more useful in the long run.

Thanks to Gavin for publishing data!

Answer 2

Is there something that does not satisfy

 split(dat, dat$cond) 

? You know that you have R and are split like tags ...

Answer 3

Yes, split() . For example, if your data is in dat , then:

 with(dat, split(dat, cond)) 

returns a list whose components are the data frames you need:

 R> with(dat, split(dat, cond)) $`1` sub cond trial time01 time02 1 1 1 1 2774 8845 2 1 1 2 2697 9945 9 3 1 1 4219 7891 $`2` sub cond trial time01 time02 3 1 2 1 2219 9291 4 1 2 2 3886 7890 6 2 2 1 3478 8827 7 2 2 2 2263 8321 $`3` sub cond trial time01 time02 5 1 3 1 4011 9032 8 2 3 1 4312 7576 10 3 3 1 3992 6674 

Answer 4

Just for completeness, here is a way to do this with the plyr package.

 require(plyr) > dlply( dat, .(cond)) $`1` sub cond trial time01 time02 1 1 1 1 2774 8845 2 1 1 2 2697 9945 9 3 1 1 4219 7891 $`2` sub cond trial time01 time02 3 1 2 1 2219 9291 4 1 2 2 3886 7890 6 2 2 1 3478 8827 7 2 2 2 2263 8321 $`3` sub cond trial time01 time02 5 1 3 1 4011 9032 8 2 3 1 4312 7576 10 3 3 1 3992 6674 attr(,"class") [1] "split" "list" 

Note the syntactic simplicity in that you only mention dat once.

Answer 5

;)

 ucond <- unique(dat$cond) dat_by_cond <- lapply(lapply(ucond, "==", dat$cond), subset, x=dat) names(dat_by_cond) <- paste("dat",ucond,sep=".")