# whichVector.logical

From R.utils v2.0.0
by Henrik Bengtsson

##### Identifies TRUE elements in a logical vector

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.- Keywords
- methods, internal, programming

##### Usage

```
## S3 method for class 'logical':
whichVector(x, na.rm=TRUE, use.names=TRUE, ...)
```

##### Arguments

##### Value

##### Benchmarking

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.

##### See Also

`which`

()

##### Examples

```
# - - - - - - - - - - - - - - - - - - - - - - - - - -
# 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));
```

*Documentation reproduced from package R.utils, version 2.0.0, License: LGPL (>= 2.1)*

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