R: Ordering vectors

order2 {grr} | R Documentation

## Ordering vectors

### Description

Simplified implementation of `order`. For large vectors, typically is about 3x faster for numbers and 20x faster for characters.

### Usage

    order2(x)

### Arguments

`x` | a vector of class numeric, integer, character, factor, or logical. Long vectors are not supported.

### Examples

    chars<-as.character(sample(1e3,1e4,TRUE))
    system.time(a<-order(chars))
    system.time(b<-order2(chars))
    identical(chars[a],chars[b])

    ints<-as.integer(sample(1e3,1e4,TRUE))
    system.time(a<-order(ints))
    system.time(b<-order2(ints))
    identical(ints[a],ints[b])

    nums<-runif(1e4)
    system.time(a<-order(nums))
    system.time(b<-order2(nums))
    identical(nums[a],nums[b])

    logs<-as.logical(sample(0:1,1e6,TRUE))
    system.time(a<-order(logs))
    system.time(b<-order2(logs))
    identical(logs[a],logs[b])

    facts<-as.factor(as.character(sample(1e3,1e4,TRUE)))
    system.time(a<-order(facts))
    system.time(b<-order2(facts))
    identical(facts[a],facts[b])

    #How are special values like NA and Inf handled?
    #For numerics, values sort intuitively, with the important note that NA and
    #NaN will come after all real numbers but before Inf.
    (function (x) x[order2(x)])(c(1,2,NA,NaN,Inf,-Inf))
    #For characters, values sort correctly with NA at the end.
    (function (x) x[order2(x)])(c('C','B',NA,'A'))
    #For factors, values sort correctly with NA at the end.
    (function (x) x[order2(x)])(as.factor(c('C','B',NA,'A')))

    #Ordering a data frame using order2
    df<-data.frame(one=as.character(1:4e5),
       two=sample(1:1e5,4e5,TRUE),
       three=sample(letters,4e5,TRUE),stringsAsFactors=FALSE)
    system.time(a<-df[order(df$one),])
    system.time(b<-df[order2(df$one),])
    system.time(a<-df[order(df$two),])
    system.time(b<-df[order2(df$two),])

    ## Not run:
    chars<-as.character(sample(1e5,1e6,TRUE))
    system.time(a<-order(chars))
    system.time(b<-order2(chars))

    ints<-as.integer(sample(1e5,1e6,TRUE))
    system.time(result<-order(ints))
    system.time(result<-order2(ints))

    nums<-runif(1e6)
    system.time(result<-order(nums))
    system.time(result<-order2(nums))

    logs<-as.logical(sample(0:1,1e7,TRUE))
    system.time(result<-order(logs))
    system.time(result<-order2(logs))

    facts<-as.factor(as.character(sample(1e5,1e6,TRUE)))
    system.time(a<-order(facts))
    system.time(b<-order2(facts))
    identical(facts[a],facts[b])

    ## End(Not run)

[Package grr version 0.9.5 Index]