Identifies TRUE elements in a logical vector
Identifies TRUE elements in a logical vector.
## S3 method for class 'logical' whichVector(x, na.rm=TRUE, use.names=TRUE, ...)
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:
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# Simulate two large named logical vectors,
# one with missing values one without
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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
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# Validate consistency
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stopifnot(identical(which(x), whichVector(x)))
stopifnot(identical(which(y), whichVector(y)))
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# Benchmarking
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# 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))
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