[R] all.equal() and which()

[Marc Schwartz (via MN)]

On Fri, 2006-02-03 at 10:41 -0500, tom wright wrote:
> Please excuse the lack of a complete dataset here, if its needed I'll be
> happy to provide it.
> Can anyone show me how to rewrite this?
> 
> Browse[1]> time(data)[24210:24220]
> [1] 24.209 24.210 24.211 24.212 24.213 24.214 24.215 24.216 24.217 
> [10] 24.218 24.219
> 
> Browse[1]> which(time(data)==24.211)
> numeric(0)
> 
> I'm assuming its an eps fault but
> which(all.equal(time(data),24.211))
> 
> dosnt seem to work


There might be an easier way, but here is one approach:

> mydat
 [1] 24.209 24.210 24.211 24.212 24.213 24.214 24.215 24.216 24.217
[10] 24.218 24.219

> which(sapply(mydat, function(x) isTRUE(all.equal(24.211, x))))
[1] 3


This uses sapply() to check each element of 'mydat' against the target
value of 24.211.  The use of 'isTRUE(all.equal(...))' returns a boolean
result of either TRUE or FALSE, enabling the use of which() against the
vector returned from sapply():

> sapply(mydat, function(x) isTRUE(all.equal(24.211, x)))
 [1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

See ?all.equal and ?isTRUE for more information.

HTH,

Marc Schwartz