whichVector.logical {R.utils} | R Documentation |
Identifies TRUE elements in a logical vector.
NOTE: which
() should be used instead of this method
unless you are running R (< 2.11.0), for which this method is faster
than which
() for logical
vector
s, especially when there
are no missing values.
## S3 method for class 'logical' whichVector(x, na.rm=TRUE, use.names=TRUE, ...)
x |
|
na.rm |
If |
use.names |
If |
... |
Not used. |
Returns an integer
vector
of length less or equal to N.
In R v2.11.0 which
() was made approx. 10 times
faster via a native implementation. Because of this, this
method is of little use and approximately 3 times slower.
However, for earlier version of R, this method is still
significantly faster. For example,
simple comparison on R v2.7.1 on Windows XP, show that
this implementation can be more than twice as fast as
which
(), especially when there are no missing
value (and na.rm=FALSE
) is used.
Henrik Bengtsson
which
()
## Not run: # - - - - - - - - - - - - - - - - - - - - - - - - - - # Simulate two large named logical vectors, # one with missing values one without # - - - - - - - - - - - - - - - - - - - - - - - - - - N <- 1e6; # Vector #1 x <- sample(c(TRUE, FALSE), size=N, replace=TRUE); names(x) <- seq_along(x); # Vector #2 y <- x y[sample(N, size=0.1*N)] <- NA; # - - - - - - - - - - - - - - - - - - - - - - - - - - # Validate consistency # - - - - - - - - - - - - - - - - - - - - - - - - - - stopifnot(identical(which(x), whichVector(x))); stopifnot(identical(which(y), whichVector(y))); # - - - - - - - - - - - - - - - - - - - - - - - - - - # Benchmarking # - - - - - - - - - - - - - - - - - - - - - - - - - - # Number of iterations K <- 5; t1 <- 0; for (kk in 1:K) { t1 <- t1 + system.time({ idxs1 <- which(x) }); }; t2 <- 0; for (kk in 1:K) { t2 <- t2 + system.time({ idxs2 <- whichVector(x, na.rm=FALSE) }); }; cat(sprintf("whichVector(x, na.rm=FALSE)/which(x): %.2f\n", (t2/t1)[3])); stopifnot(identical(idxs1, idxs2)); t1 <- 0; for (kk in 1:K) { t1 <- t1 + system.time({ idxs1 <- which(y) }); }; t2 <- 0; for (kk in 1:K) { t2 <- t2 + system.time({ idxs2 <- whichVector(y) }); }; cat(sprintf("whichVector(y)/which(y): %.2f\n", (t2/t1)[3])); stopifnot(identical(idxs1, idxs2)); ## End(Not run)