Whats the difference between Cases and Select?

Question

Im trying to further my understanding of mathematica coding and came up across this question. What is the main difference between Cases and Select?

data = Table[{RandomReal[{-10, 10}], RandomReal[{-10, 10}], RandomReal[{-10, 10}]}, 10^4];
Cases[data, {a_, b_, c_} :> {a, b} /; c > 0]
Select[data, #[[3]] > 0 &][[All, ;; 2]]

Both these approaches give the same result, Im just curious about the benefits of each. When is Select superior to Cases and vice versa.

Possible duplicate: What best practices or performance considerations are there for choosing between Cases, Position, Pick and Select?. Also this: Cases vs Select, Pattern vs Pure function — Vitaliy Kaurov, Sep 17 '18 at 17:18
How about Pick[data, UnitStep[data[[All, 3]]], 1] for speed? — Szabolcs, Sep 17 '18 at 18:02

Henrik Schumacher · Accepted Answer · 2018-09-17T17:26:53.640

3

Cases uses patterns, Select uses testing functions. Because of this, Select is not seldomly faster because it reduces pattern matching to the very least: Does the testing function evaluate to True or not? (Pattern matching can be a real bottleneck sometimes, inparticular if the mere check for matching enforces unpacking of arrays.)

On the other hand, Cases is much more flexible.

1.) Cases allows a level specification. (Select always operates on the first level of an expression)

2.) Cases allows to apply replacement rules immediately.

edited Sep 17 '18 at 17:26

answered Sep 17 '18 at 17:18

Henrik Schumacher

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Thanks @Alan. It was a typo. – Henrik Schumacher Sep 17 '18 at 17:27

Whats the difference between Cases and Select?

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