[R] x %>% y as an alternative to which( x > y)

[Duncan Murdoch]

On 13/09/2011 12:42 PM, Timothy Bates wrote:
> Dear R cognoscenti,
>
> While having NA as a native type is nifty, it is annoying when making binary choices.
>
> Question: Is there anything bad about writing comparison functions that behavior like %in% (which I love) and ignore NAs?
>
> "%>%"<- function(table, x) {
> 	return(which(table>  x))
> }
>
> "%<%"<- function(table, x) {
> 	return(which(table<  x))
> }
>
> test<- c(NA, 1:4,NA,5)
> test %>% 2
> # [1] 3 4 6
> test %<% 2
> # [1] 1
>
> Why do I want to do this?
>
> Because in coding, I often end up with big chunks looking like this:
>
> ((mydataframeName$myvariableName>  2&  !is.na(mydataframeName$myvariableName))&  (mydataframeName$myotherVariableName == "male"&  !is.na(mydataframeName$myotherVariableName)))
>
> Which is much less readable/maintainable/editable than
>
> mydataframeName$myvariableName>  2&  mydataframeName$myotherVariableName == "male"
>
> But ">" returns anything involving an NA, so it breaks selection statements (which can't contain NA) and leaves lines in data that are wished to be excluded
>
> If this does not have nasty side-effects, it would be a great addition to GTD* in R
>
> If anyone knows a short cut to code the effect I wish, love to hear it.

I would suggest subsetting first if you really want to ignore the NAs.

A problem with your suggestion is that since it doesn't return a logical 
vector, it will behave quite differently from a standard comparison in 
an expression.  For example

(a < 5) & (b < 6)

will work (but sometimes generate NAs), but

(a %<% 5) & (b %<% 6)

will not.  (You'd need to use the intersect() function.)

Duncan Murdoch

> Cheers,
> tim
>
> * GTD = Getting Things Done
>
>