whichVector.logical

0th

Percentile

Identifies TRUE elements in a logical vector

Identifies TRUE elements in a logical vector. This method is faster than which() for logical vectors, especially when there are no missing values.

Usage
## S3 method for class 'logical}(x, na.rm=TRUE, use.names=TRUE, ...)':
whichVectorundefined

 x{A logical vector of length N.}
   na.rm{If TRUE, missing values are treated as FALSE,
      otherwise they are returned as NA.}
   use.names{If TRUE, the names attribute is preserved,
      otherwise it is not return.}
   ...{Not used.}

 Returns an integer vector of length less or equal to N.

 
Benchmarking
{ 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. } # - - - - - - - - - - - - - - - - - - - - - - - - - - # Simulate two large named logical vectors, # one with missing values one with out # - - - - - - - - - - - - - - - - - - - - - - - - - - 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 ", (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 ", (t2/t1)[3])); stopifnot(identical(idxs1, idxs2)); [object Object] which() methods programming
Aliases
  • whichVector.logical
  • whichVector.logical
  • whichVector.matrix
Documentation reproduced from package R.utils, version 1.1.0, License: LGPL (>= 2.1)

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