0 is the initial value of a.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce

Drop the caps, please.

The instructions were unclear. I needed to read the comments for them.

YOU ARE GIVEN 2 LISTS: ONE OF GEESE AND ANOTHER ONE TO MODIFY. YOU MUST REMOVE THE GEESE FROM THE SECOND LIST.

Thank you, worked!

It seems you messed up the sample tests, backup your code, click Reset, paste it and try again, they should look like this:

describe("Basic tests",function(){
  it("Mixed list",function(){
    Test.assertDeepEquals(gooseFilter(["Mallard", "Hook Bill", "African", "Crested", "Pilgrim", "Toulouse", "Blue Swedish"]),["Mallard", "Hook Bill", "Crested", "Blue Swedish"]);
  });
  it("No geese",function(){
    Test.assertDeepEquals(gooseFilter(["Mallard", "Barbary", "Hook Bill", "Blue Swedish", "Crested"]),["Mallard", "Barbary", "Hook Bill", "Blue Swedish", "Crested"]);
  });
  it("All geese",function(){
    Test.assertDeepEquals(gooseFilter(["African", "Roman Tufted", "Toulouse", "Pilgrim", "Steinbacher"]),[]);
  });
});

Thanks! Will try again

you are not required to (and should not) mutate the input matrix; your algo is wrong. try your function with e.g. [[1, 2], [3, 4]], it returns [ [ 1, 3, 1, 3 ], [ 2, 4, 2, 4 ] ], which is not the transpose of [[1, 2], [3, 4]]

JavaScript

What language?

Hi! My preliminary test gets green but then stops with this message:

expected [ [ 1, 4, 1, 4 ], [ 2, 5, 2, 5 ], [ 3, 6, 3, 6 ] ] to deeply equal [ [ 1, 4, 7 ], [ 2, 5, 8 ], [ 3, 6, 9 ] ]

I don't understand why should I have to mutate the values as it's not required in the instructions. Also I am testing with strings e.g. 'a', 'b', 'c' etc. and it works perfectly. I understand I just need rebuild the rows replacing the positions and changing lengths. Maybe this kata lacks in more detailed instructions? I'm trying to trunckate redundant numbers from the input rows... Any help is welcome :)

Read this: https://docs.codewars.com/training/troubleshooting/#works-but-no

Don't use global vars, they keep their values between tests. If you call your function several times in a row in your IDE it'll fail there too.

My code' output too is 4 years, 68 days, 3 hours and 4 minutes

Hi, why you added the 0 after 'a + b' ?