From maechler at stat.math.ethz.ch  Mon May 16 10:43:30 2011
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Mon, 16 May 2011 10:43:30 +0200
Subject: [Rd] Add "See Also:  missing" to help('exists')?
In-Reply-To: <4DCE69E0.4070107@prodsyse.com>
References: <4DCE2F89.2090503@global-analytics.com>
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	<4DCE69E0.4070107@prodsyse.com>
Message-ID: <19920.58290.687681.804857@stat.math.ethz.ch>


    SpG>        Might it be feasible to add, "See Also: missing"
    SpG> to the help page for "exists"?


    SpG>        Currently, one can spend hours studying the help
    SpG> page for "exists" without getting a clue to the answer
    SpG> to the post copied below.

Yes. I've added such a link now...
though quite disillusioned with a very vague hope that useRs
would read the help page so thoroughly ...

Martin Maechler, ETH Zurich

    SpG>        Thanks, Spencer


    SpG> On 5/14/2011 3:30 AM, David Winsemius wrote:
    >> 
    >> On May 14, 2011, at 3:30 AM, utkarshsinghal wrote:
    >> 
    >>> 
>>   Hi all,
>>   I want to define a function such that one of its argument if passed 
>> do one
>>   thing and if not passed do the second thing.
>
> ?missing
>
>> So basically, I have to check
>>   whether the argument is passed or not inside the function. I am 
>> trying to
>>   use 'exists' function to do this.
>>> f = function(a,b){exists("b")}
>>> f(a=3, b=4)
>>   [1] TRUE
>>   This is working as expected.
>>   But if I do the following:
>>> f(a=3)
>>   [1] TRUE
>>   Can anybody explain why this function is returning TRUE here.
>> -- 
>> Many thanks,
>> Utkarsh

>>...

> David Winsemius, MD
> West Hartford, CT



[Rd] Add "See Also: missing" to help('exists')?
Martin Maechler