6 kyu
Array#reduce
4,243 of 4,417user578387
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Functional Programming
Algorithms
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https://www.codewars.com/kumite/645eae46d3560e0013c3c01e?sel=645eae46d3560e0013c3c01e
Here is a translation to update the
assertSimilarcalls toassertDeepEquals, in order to remove warnings when running the code.Please feel free to review and approve. Thanks.
approved
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No random tests
Node 12 should be enabled
Expected: 'fallaffles', instead got: 'undefinedaffles'.
JavaScript at its finest :)
This does not work like the real reduce as the top answer would ignore falsy initial values and assign the first element instead.
It also does not test the callback to make sure it has the standard four arguments.
Need more test cases.
The initial test in coffeescript is wrong. It reduces to "say!" but tests against "yay!".
Fixed. Thanks for reporting.
I learned a lot about reduce from the famous paper why functional programming matters. It's really a awesome paper. The reduce in js and this kata is somehow not exactly the reduce explained in the paper.
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Thanks! Adding right now.
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If I call
[1,2,3].reduce( f, nil )it should dof( f( f(nil, 1), 2), 3)- Your function seems to treatnilas the test for an undefined starting point, but that shouldn't be the case.For
[1,2,3].reduce( f, nil ):f.( f.( f.( nil, 1), 2), 3)f.( f.( 1, 2), 3)I see it now. Thanks for the clarification!
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Hm, I think I overkilled! I'll sort that out.
EDIT: I originally implemented that last test to sort out people who had copied from somewhere, but I havn't seen many of those, so I'll leave it.
Most solutions handle
nilas a second argument incorrectly.[true].reduce( ->(m, s) { m && s }, nil)should benil, but these solutions returntrue. Perhaps a test should be added for this.Added!
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Implemented, thanks!
I think
Array#reduceshould not modify array objectThis comment has been hidden.
Undefined
Array#inject.Actualy, reduce callback function in javascript is called with four parameters - accumulator, element value, element index and reference to array. Maybe you implement this for javascript and coffeescript (but not for ruby)? And also give a link to reduce method documentation in kata description.
Good suggestion, but for simplicity's sake, we'll keep the kata specification as it is. Besides, I've found people cheat by copying the code on Mozilla, so having a case the same as that would be hard to regulate!
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Resolved!
You should do some order-specific tests, and make sure the correct values are passed to the
processfunction, and in the correct order.You could also add tests for when no
initialvalue has been given, or even when noprocesswas given. (Maybe expect an error?)I like the idea of
initialvalue defaults, but how do you suggest testing order-specificity?(Edit: implemented
initialdefaults)Well, in the code:
we expect the following calls:
If these calls are made out of order, or some are missing, or the result is different, the reduce method doesn't work properly.
As for an unspecified
initialvalue, you should go by the JS spec for the reduce method to reduce confusion. Basically, the initial value would be assumed to be the first value in the array, so:Allright, I think the string tests work well as order tests, and the default
initialis implemented: resolved!I cheated - you might want to disable
Array.prototype.reduceRightas well.Resolved, thanks for telling me!