CountBy Method into a Function Using Javascript
I'm Trying to Write a countBy Function, Identical to the countBy Method in Javascript. Here Is What I Have So Far: Var Array = [1,2,4,4,5]; Function...
I'm trying to write a countBy function, identical to the countBy method in Javascript. Here is what I have so far:
var array = [1,2,4,4,5];
function countBy(collection, func) {
var object = {} ;
for (var i=0;i<=0; i++) {
for (var key in object) {
if (func(collection[i]) === object.key) {
object.key ++;
} else {
object.key = 1;
}
}
}
return object
}
alert(countBy(array, function(n) {return Math.floor(n);}));
What the code intends to do is search through the collection array to see if a value there matches a key in object. If it has found a match in the collection array, increment that key value by one. If it has not found one, create a new key value. Therefore, the result that should be alerted is: {4:2, 1:1, 2:1, 5:1}. But it seems like my output is [object Object]. What am I doing wrong??
2 Answers
for (var i=0;i<=0; i++) {
This will run exactly once instead of iterating through the collection.
for (var key in object) {
if (func(collection[i]) === object.key) {
This does the wrong thing; you should call func only once in each iteration and then look up the result of the function call in your object.
object.key ++;
This doesn't do what you want; it's better to use the array dereference operator instead.
function countBy(collection, func)
{
var object = Object.create(null);
collection.forEach(function(item) {
var key = func(item);
if (key in object) {
++object[key];
} else {
object[key] = 1;
}
});
return object;
}
function countby(arr, selector) {
selector = selector ?? (x => x) // default is identity
const f = (acc, x) => {
let k = selector(x);
acc[k] = (acc[k] ?? 0) + 1;
return acc
}
return arr.reduce(f, {})
};
let r
r = countby([2, 3, 1, 3, 4, 4])
console.log(r)
r = countby([{a:2}, {a:3, b:"bunny"}, {a:2}], (x => x.a))
console.log(r)Robert Thorne covers electric vehicle innovations, autonomous driving systems, global mobility trends, and automotive engineering developments.
