

   EExxttrraacctt SSuubbssttrriinnggss ffrroomm aa CChhaarraacctteerr VVeeccttoorr

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

   DDeessccrriippttiioonn::

        `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 argu-
        ments, it expands the arguments cyclically.

   SSeeee AAllssoo::

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

   EExxaammpplleess::

        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)

