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Re: Cost of Composition vs Pure Function


On Nov 20, 2008, at 4:56 AM, Raffy wrote:

> The speed difference between these two evaluations seems odd,
> considering they are effectively the same thing:
>
> m = RandomReal[{0, 1}, {10, 1000, 1000}];
>
> Total[Total[#]]& /@ m; // Timing => 0.14 sec
>
> Composition[Total, Total] /@ m; // Timing => 0.983 sec
>
> Other than the Identity and Inverse Function transformation, where is
> this overhead coming from?

I think it's from Composition, due to order of operations the  
composition is being done for each row of m as the pure function is  
mapped, not before the mapping.

Regards,

Sseziwa


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