[R] force apply() to return a list

[Robin Hankin]

Hi

I have a function f() that I want to apply() to a matrix.  I want the
answer to be a list.

However, sometimes all the vectors returned by f() are the same length
and apply() returns a matrix.  I do not want this.

Hi

How do I force apply() to consistently return a list?
Toy example follows.

R> f <- function(x){1:max(x[1],4)}
R> a1 <- cbind(1:5,5:1)
R> apply(a1,1,f)
[[1]]
[1] 1 2 3 4

[[2]]
[1] 1 2 3 4

[[3]]
[1] 1 2 3 4

[[4]]
[1] 1 2 3 4

[[5]]
[1] 1 2 3 4 5

list returned: desired behaviour.  Now try the
same but with a different matrix from a1:


R> a2 <- cbind(1:3,3:1)
R> apply(a2,1,f)
      [,1] [,2] [,3]
[1,]    1    1    1
[2,]    2    2    2
[3,]    3    3    3
[4,]    4    4    4


matrix returned: this is undesired behaviour (in my application, I
pass the list to do.call()).  How do I force apply() to behave
consistently and return a list, irrespectively of the length of
vectors returned by f()?



--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743