Reshape matrix into a list of lists

Question

I have a list as follows:

 id | value
 ----------
  4     600
  4     899
  7      19
 13    4930
 13     300
  :       :

There are multiple ID

Answer 1

You could also use tapply if you want to stick with base functions:

tapply(dat$value,dat$id,c)
$`4`
[1] 600 899

$`7`
[1] 19

$`13`
[1] 4930  300

Edit:

For your edited problem, I would go with split and lapply:

x <- lapply(split(dat[2:3],dat$id),c,use.names=F)

dput(x)
structure(list(`4` = list(c(600, 899), c("a", "b")), `7` = list(
19, "d"), `13` = list(c(4930, 300), c("e", "a"))), .Names = c("4", "7", "13"))