How can I use more than one function to filter an array in javascript?

Question

I want to use filter1 and filter2 functions in generalFilter but I can't comprehend the right syntax to do it in Javascript.

const filter1 = (
  array
) => {

  return array.filter((parameter, index) => {
    return (
      !parameter.isOptional()
    );
  });
};

const filter2 = (
  array
) => {

  return array.filter((parameter, index) => {
    return (
      !parameter.isEmpty()
    );
  });
};

const filterGeneral = (
  array
) => {
  return array.filter(filter1(array) && filter2(array));
};

This is apprx. what I am trying to do but I am not able to manage to succeed, and I didn't like my logic. Is there any way to do this properly?

array.filter(func1).filter(func2)

Jeremy Thille
– Jeremy Thille

2020-03-20 13:36:31 +00:00
Commented Mar 20, 2020 at 13:36 — Jeremy Thille
– Jeremy Thille, Commented Mar 20, 2020 at 13:36

Nina Scholz · Accepted Answer · 2020-03-20 13:41:06Z

4

You could use a pipe function, where you take some function and take the result from the first function as input for the second function, and so on.

const
    pipe = (...functions) => input => functions.reduce((acc, fn) => fn(acc), input),
    filter1 = array => array.filter((parameter, index) => !parameter.isOptional()),
    filter2 = array => array.filter((parameter, index) => !parameter.isEmpty()),
    filterGeneral = pipe(filter1, filter2),
    array = [{ ... }, { ... }],
    result = filterGeneral(array);

answered Mar 20, 2020 at 13:41

Nina Scholz

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2 Comments

SteapStepper69 Over a year ago

Very intersting approach, why (if it is) is this better than just chaining multiple filter functions?

Nina Scholz Over a year ago

it works with any type, because it is independent of array's prototype functions.

FabioFLX · Accepted Answer · 2020-03-20 13:36:53Z

2

Has they are two different filters, you can only apply one at a time over the parameter itself, so I think you should apply one to another:

const filterGeneral = array => filter1(filter2(array));

answered Mar 20, 2020 at 13:36

FabioFLX

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1 Comment

Andy Over a year ago

I would probably filter first by filter1 then filter2.

SteapStepper69 · Accepted Answer · 2020-03-20 13:41:37Z

1

You can just chain multitple filter() methods like this:

const array = [1, 2, 3, 4, 5];

array.filter((elem) => elem > 2).filter((elem) => elem > 3);
// returns [4, 5]

This works because Array.prototype.filter() returns the filtered array. You can just filter this array again.

This means that the example above is the same as writing this:

const array = [1, 2, 3, 4, 5]
const tmp = array.filter((elem) => elem > 2);
tmp.filter((elem) => elem > 3);

edited Mar 20, 2020 at 13:41

answered Mar 20, 2020 at 13:36

SteapStepper69

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2 Comments

Andy Over a year ago

The functions do the acual filtering, so it doesn't make sense to pass them into .filter as a callback.

SteapStepper69 Over a year ago

@Andy I just realised right after hitting answer and edited my answer

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