[Rd] apply() returning a list?

David A. Johnston dajohnston at ucdavis.edu
Wed Jul 20 01:34:53 CEST 2011

Hi devel list,

I searched for past posts about this issue and found none, so my apologies
if this has been addressed before.  

The sapply() function has an argument 'simplify', and the mapply() function
has an argument 'SIMPLIFY'.  I am surprised that the apply() argument does
not have a similar argument.  Is there a reason for this?  

Here's a simple example:
> x = matrix(1:12, 3, 4)
> apply(x, 1, sum)
[1] 22 26 30

This is what I would like to see:
> apply(x, 1, sum, simplify = FALSE) 
[1] 22

[1] 26

[1] 30

Looking at the function definition of apply(), I imagine it wouldn't be too
hard to add such an argument.  Add an argument 'simplify' with default value
TRUE, and include the following line in the function definition.
if(simplify == FALSE)  return (ans)

Is this a good idea? Would this be a good addition to R's apply() function?
Are there stability issues in making this change (for example, what if some
previous code threw a 'simplify' argument into the '...')?


-David Johnston

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