If I have two arrays as parameters how can I find the starting index where the second parameter occurs as a sub-array in the array given as the first parameter.
E.g.: [5,9,3,6,8], [3,6] should return 2.
Is there a function in JavaScript for this, or does it just loop through both of them and compare?
findArrayInArray = function(a, b) {
var ai = a.length
, bi = b.length;
for(var i=0; i<ai; i++) {
if (a[i] === b[0]) {
if(bi === 1) return i;
for(var x=1; x<bi; x++) {
if(a[i+x] === b[x]) {
if(x === bi-1) return i;
} else {
break;
}
}
}
}
}
var arr1 = [5,9,3,6,8];
var arr2 = [3,6];
console.log(findArrayInArray(arr1,arr2)); // 2
arr2.length == 1,
In direct answer to your question, there is no built in function in JS to look in an array for a sub-array.
You will have to do some sort of brute force looping search like this or use some external library function that already has array comparison logic. Here's what a brute force solution in plain JS looks like:
function findSubArrayIndex(master, sub) {
for (var m = 0; m < master.length - sub.length + 1; m++) {
for (var s = 0; s < sub.length; s++) {
if (master[m + s] !== sub[s]) {
break;
} else if (s === sub.length - 1) {
return m;
}
}
}
return -1;
}
Working demo: http://jsfiddle.net/jfriend00/mt8WG/
FYI, here's a somewhat performance optimized version of this function:
function findSubArrayIndex(master, sub) {
var subLen = sub.length, subFirst, m, mlen;
if (subLen > 1) {
subFirst = sub[0];
for (m = 0, mlen = master.length - subLen + 1; m < mlen; m++) {
if (master[m] === subFirst) {
for (var s = 1; s < subLen; s++) {
if (master[m + s] !== sub[s]) {
break;
} else if (s === subLen - 1) {
return m;
}
}
}
}
} else if (subLen === 1) {
subFirst = sub[0];
for (m = 0, mlen = master.length; m < mlen; m++) {
if (master[m] === subFirst) {
return m;
}
}
}
return -1;
}
Working demo: http://jsfiddle.net/jfriend00/CGPtX/
function index (a, b) {
var as = new String(a),
bs = new String(b),
matchIndex = as.indexOf(bs);
if (matchIndex === -1) {
return -1;
} else if (matchIndex === 0) {
return 0;
}
return as.substring(0, matchIndex + 1).match(/,/g).length;
}
console.log(index([5,9,3,6,8], [3, 6]));
0 if the second arg is an empty array - not sure what the function should return for that case. My answer chose to return -1 if the second arg is a zero, but I guess it isn't really specified how that should be handled.you could try this
function compareArray(arr1, arr2){
return arr1.join("") == arr2.join("");
}
this code returns true if the array and its contents are the same and false if the arrays and its contents are not the same
You can use the javascript built-in String.indexOf method by converting this array to a string.
function subArrIndex(arr, subArr) {
let a1 = arr.join(" ");
let a2 = subArr.join(" ")
let index = a1.indexOf(a2);
let subStringEarlier = a1.substr(0, index);
// count number of spaces ' '
return subStringEarlier.split(' ').length - 1;
}
let arr = [5,9,3,6,8]
let subArr= [3,6]
console.log(subArrIndex(arr, subArr));It will not work if the array contains space ' '. You can then use some other delimiter like , or \n.
let array1 = [11, 22, 33];
let array2 = [21, 22, 23];
let array3 = [11, 22, 33];
const compareArray = (a, b) => {
return JSON.stringify(a) === JSON.stringify(b);
};
console.log(compareArrays(array1, array2));
console.log(compareArrays(array1, array3));
Try this - You loop through both arrays and compare each element:
var arr1 = [5,9,3,6,8];
var arr2 = [3,6];
findArrayInArray = function(arr1, arr2) {
for(var i=0; i<arr1.length; i++) {
for(var j=0; j<arr2.length; j++){
if(arr1[i] === arr2[j]){
return i;
}
}
}
return false;
}
findArrayInArray(arr1, arr2);
arr2.length == 1 because it never compares beyond the first item in arr2.
if(arr1[i] === arr2[j]){, your function returns. It never compares the rest of arr2.arr2, not just the first item in arr2. Look at what it returns here: jsfiddle.net/jfriend00/kLLrd