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Find number of elements less than some number: Elegant/fastsolution needed

William Dunlap 
If x is sorted findInterval(x, y) would do it for <= but you
want strict <.  Try
  f2 <- function(x, y) length(y) - findInterval(-x, rev(-sort(y)))
where your version is
  f0 <- function(x, y) sapply(x,FUN=function(i) {length(which(y<i))})
E.g.,
  > x <- sort(sample(1e6, size=1e5))
  > y <- sample(1e6, size=1e4, replace=TRUE)
  > system.time(r0 <- f0(x,y))
     user  system elapsed
    7.900   0.310   8.211
  > system.time(r2 <- f2(x,y))
     user  system elapsed
    0.000   0.000   0.004
  > identical(r0, r2)
  [1] TRUE

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

Thread (9 messages)

Kevin Ummel Find number of elements less than some number: Elegant/fast solution needed Apr 14 Richard M. Heiberger Find number of elements less than some number: Elegant/fast solution needed Apr 14 Marc Schwartz Find number of elements less than some number: Elegant/fast solution needed Apr 14 Gustavo Carvalho Find number of elements less than some number: Elegant/fast solution needed Apr 14 William Dunlap Find number of elements less than some number: Elegant/fastsolution needed Apr 14 Douglas Bates Find number of elements less than some number: Elegant/fastsolution needed Apr 14 Ravi Varadhan Find number of elements less than some number: Elegant/fastsolution needed Apr 14 Douglas Bates Find number of elements less than some number: Elegant/fastsolution needed Apr 14 Ray Brownrigg Find number of elements less than some number: Elegant/fastsolution needed Apr 14