# [R] Multiple if function

Bert Gunter bgunter.4567 at gmail.com
Wed Sep 16 23:17:43 CEST 2015

```I assume it's to return the vectors in their original order.

-- Bert

Bert Gunter

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
-- Clifford Stoll

On Wed, Sep 16, 2015 at 2:10 PM, David Winsemius <dwinsemius at comcast.net> wrote:
>
> On Sep 15, 2015, at 7:20 PM, Charles C. Berry wrote:
>
>> On Tue, 15 Sep 2015, Bert Gunter wrote:
>>
>>> Thanks to both Davids.
>>>
>>> I realize that these things are often a matter of aesthetics -- and
>>> hence have little rational justification -- but I agree with The Other
>>> David: eval(parse) seems to me to violate R's soul( it makes R a macro
>>> language instead of a functional one).
>>>
>>> However, mapply(... switch) effectively loops through the frame row by
>>> row. Aesthetically, I like it; but it seems inefficient. If there are
>>> e.g. 1e6 rows in say 10 categories, I think Jeff's approach should do
>>> much better.  I'll try to generate some actual data to see unless
>>> someone else beats me to it.
>>
>> Use mapply like this on large problems:
>>
>> unsplit(
>>    mapply(
>>        function(x,z) eval( x, list( y=z )),
>>        expression( A=y*2, B=y+3, C=sqrt(y) ),
>>        split( dat\$Flow, dat\$ASB ),
>>        SIMPLIFY=FALSE),
>>    dat\$ASB)
>>
>
> Seems unnecessarily complex, but definitely elegant. Was there a reason it was not just:
>
> mapply(
>        function(x,z) eval( x, list( y=z )),
>        expression(A= y*2, B=y+3, C=sqrt(y) ),
>        split( dat\$Flow, dat\$ASB )
>      )
>
> Also readers should note that the names in that expression vector are quite arbitrary at the moment. The only association is via the order. I don't suppose someone wants to take on the challenge of matching the names of the expression vector with the names of returned split components?
>
>
>> Chuck
>
> David Winsemius
> Alameda, CA, USA
>

```