Re: Applying a function to selected element type in a mixed-type cell array

[Juan Pablo Carbajal]

On Tue, May 22, 2012 at 3:50 PM, Jordi Gutiérrez Hermoso
<address@hidden> wrote:
> On 22 May 2012 03:05, Juan Pablo Carbajal <address@hidden> wrote:
>> On Tue, May 22, 2012 at 12:56 AM, Philip Nienhuis <address@hidden> wrote:
>>> Ben Abbott wrote:
>>>>
>>>>
>>>> On May 21, 2012, at 5:43 PM, Philip Nienhuis wrote:
>>>>
>>>>> Suppose a cell array like:
>>>>>
>>>>> arr = {10, int32(15), 'Txt'; '', 25, true; NaN, 'String', single(100)}
>>>>>
>>>>> How can all numeric values efficiently (w/o for loops etc.) be converted
>>>>> to double, leaving the other cell array contents untouched?
> [snip]
>>>> A Two-liner ?
>>>>
>>>>        n = cellfun (@isnumeric, arr, "UniformOutput", true);
>>>>        arr(n) = cellfun (@double, arr(n), "UniformOutput", false);
> [snip]
>> cool,
>> Can anybody explain to me why the two-liner is 3-4 times faster than
>> the function version?
>
> Basically, this:
>
>    
> http://hg.savannah.gnu.org/hgweb/octave/file/d95e719ef108/src/DLD-FUNCTIONS/cellfun.cc#l441
>
> You'll see that for certain kinds of functions, we can take a better
> code path.
>
> Come to think of it, it would be very easy to also optimise isnumeric
> in this fashion.
>
> HTH,
> - Jordi G. H.

I think I got it (mmm...). Thanks


-- 
M. Sc. Juan Pablo Carbajal
-----
PhD Student
University of Zürich
http://ailab.ifi.uzh.ch/carbajal/