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

[Max Brister]

On Tue, May 22, 2012 at 1:05 AM, 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?
>>>>
>>>> Getting at something like  "arr(find (cellfun ("isnumeric", [arr])))" is
>>>> easy enough, but the follow-up is a hazy to me.
>>>>
>>>> Thanks,
>>>>
>>>> Philip
>>>
>>>
>>> A Two-liner ?
>>>
>>>        n = cellfun (@isnumeric, arr, "UniformOutput", true);
>>>        arr(n) = cellfun (@double, arr(n), "UniformOutput", false);
>>
>>
>> Yep that'll work fast enough. I got close to something like the second line
>> myself but I guess I forgot about the '"UniformOutput", false' thing.
>>
>> BTW I need this to fix a bug in the io pkg spreadsheet writing scripts that
>> turns out to have been there from the very beginning:
>> The various Java and ActiveX methods that transfer numerical values to
>> spreadsheets accept only doubles, no int<x>, single or unsigned.
>> Not so strange when you realize that spreadsheets essentially contain just
>> boolean, double or text values (cell formatting makes for a -cosmetic- wider
>> variety). I never hit this limitation until today at work when I was
>> converting text files containing integer values into spreadsheets.
>>
>> Thanks Ben & Juan,
>>
>> Philip
>> _______________________________________________
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>
> cool,
> Can anybody explain to me why the two-liner is 3-4 times faster than
> the function version?

The overhead for calling an Octave function is greater than that of
calling a builtin function.

Max Brister