Why does Through unpack?
- To: mathgroup at smc.vnet.net
- Subject: [mg125587] Why does Through unpack?
- From: Szabolcs <szhorvat at gmail.com>
- Date: Tue, 20 Mar 2012 02:20:32 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
Consider the following example: On["Packing"] dat = RandomInteger[1*^7, {5000000, 2}]; Max /@ Transpose[dat]; // AsboluteTiming Note that the array is only unpacked to level 1, so Max is fast. Now let's get both the Min and the Max: Through /@ {Min, Max} /@ Transpose[dat]; // AbsoluteTiming Now the full array is unpacked, significantly hurting performance. Question: Why is it necessary to unpack the array when using Through? Here it doesn't seem to be. Is it a design decision that Through unpacks, or is it an over sight? Through does not touch the function argument (it only affects the head), I don't see why it would need to unpack it.
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