[R] basic question

[Marc Schwartz]

<snip>

Oops...I forgot one more, using 'test.s' as per the prior e-mail:

test.s <- split(test, test$year)

> sapply(test.s, function(x) colSums(x[, -1]))
  2000 2001
x   95  105
y   31  114
z   94   97

or transpose using t():

> t(sapply(test.s, function(x) colSums(x[, -1])))
       x   y  z
2000  95  31 94
2001 105 114 97


which is similar of course to the use of aggregate():

> aggregate(test[, -1], list(Year = test$year), sum)
  Year   x   y  z
1 2000  95  31 94
2 2001 105 114 97

The key difference is that aggregate() returns a data frame, whereas
sapply() returns a matrix in this case.

So, see ?sapply as well.

HTH,

Marc Schwartz