Filter numbers within an Array using a Function Parameter

Question

Filter numbers within an Array using a Function Parameter

I'm currently experimenting with Arrays and the .filter() function. My goal is to filter between specified parameters in a function to achieve the desired output. However, I'm encountering an issue where my NPM test is failing. Although the output appears to be correct, I keep receiving an error stating that '[object Array] is not a function at Array.filter'. Can anyone point out where I might have made a mistake?

Below is the code snippet:

function betweenArray(c, d){
    
    let filterNumbers = arr.filter(function(currentElement) {
        if (currentElement >= c && currentElement <= d)
        return currentElement 
    })

    return filterNumbers
}

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

console.log(arr.filter(betweenArray(4, 10))); // 2, 3, 4, 5, 6, 7

javascript arrays function npm

Answer 1

Answer №1

When using Array.filter, a function is required that returns either true or false (known as a predicate function). If the function returns true, the item is included in the resulting array; if it returns false, the item is excluded.

To create this predicate function, you can utilize arrow function notation like so:

const between = (min, max) => (v) => v >= min && v <= max;

You can then apply this function by filtering an array based on a range specified by the minimum and maximum values:

const between = (min, max) => (v) => v >= min && v <= max;
let arr = [-2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
console.log(arr.filter(between(-1, 3)));

Note:

The explanation behind why your initial predicate function mostly worked is due to the coercion of non-zero numbers to true and undefined to false.

However, when attempting to filter with a range spanning zero, the behavior breaks down. Let's examine how this happens:

const between = (min, max) => function(currentElement) {
  if (currentElement >= min && currentElement <= max)
    return currentElement // not `true`, but a number
  // here, `undefined` is implicitly returned
}
let arr = [-2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
console.log(arr.filter(between(-1, 3))); // zero missing!?!

Where did zero vanish to? Give it some thought and try to discern why this breakdown occurs.

Answer 2

When using Array.filter, a function is required that returns either true or false (known as a predicate function). If the function returns true, the item is included in the resulting array; if it returns false, the item is excluded.

To create this predicate function, you can utilize arrow function notation like so:

const between = (min, max) => (v) => v >= min && v <= max;

You can then apply this function by filtering an array based on a range specified by the minimum and maximum values:

const between = (min, max) => (v) => v >= min && v <= max;
let arr = [-2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
console.log(arr.filter(between(-1, 3)));

Note:

The explanation behind why your initial predicate function mostly worked is due to the coercion of non-zero numbers to true and undefined to false.

However, when attempting to filter with a range spanning zero, the behavior breaks down. Let's examine how this happens:

const between = (min, max) => function(currentElement) {
  if (currentElement >= min && currentElement <= max)
    return currentElement // not `true`, but a number
  // here, `undefined` is implicitly returned
}
let arr = [-2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
console.log(arr.filter(between(-1, 3))); // zero missing!?!

Where did zero vanish to? Give it some thought and try to discern why this breakdown occurs.

Filter numbers within an Array using a Function Parameter

Answer №1

Note:

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