## Extract Substrings from a Character Vector

## Usage

    substr(x, start, stop)
    substring(text, first, last = 1000000)

## Description

`substr` takes a character vector as an argument and returns a vector whose elements contain the substring starting with the character at position `start` up to the character at position `stop`. If `start` is larger than the string length then `NA` is returned. If `stop` is longer than `start` and error is signalled.

`substring` is compatible with S. For vector arguments, it expands the arguments cyclically.

## See Also

`strsplit`, `paste`, `nchar`.

## Examples

    substr("abcdef",2,4)
    substring("abcdef",1:6,1:6)
    substr(rep("abcdef",4),1:4,4:5)
    x <- c("asfef", "qwerty", "yuiop[", "b", "stuff.blah.yech")
    all(substr(x, 2, 5) == substring(x, 2, 5)) #> TRUE
    substr(x, 2, 5)
    substring(x, 2, 4:6)

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