[Rd] match vs. %in% (PR#853)

Prof Brian D Ripley ripley@stats.ox.ac.uk
Mon, 19 Feb 2001 07:24:55 +0000 (GMT)

On Sun, 18 Feb 2001 baron@cattell.psych.upenn.edu wrote:

> This isn't really a bug so much as an undocumented feature, but
> perhaps the help file should be changed.
> If you say
> match(x,y)
> you get the values of the _first_ instance in y that matches each
> value of x.

Yes, but one match or not for each instance of x.

> If you say
> x %in% y
> you get "TRUE" for every match, not just the first.

You get a result for each element of x, not y.

Both return a result for each element of x. match returns the index of the
first match or `nomatch',  %in% returns TRUE or FALSE.

is.element is a synonym of %in% compatible with S, which uses %in% for
something else (nesting in formulae).

> This is useful, now that I know it, but perhaps the thing
> about the first instance should be documented.

Yes, ?match needs a `details' section.  I'll add one.

Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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