This question already has answers here:
Picking 2 random elements from array
(10 answers)
Closed 7 years ago.
I have an array such as:
array=['a','b','c','d','e','f'];
I want to delete a random 2 elements. How can I do this?
To get two unique items from the array, and if you don't mind mutating the original array, you can use splice() to remove the selected item from the array so it won't be picked when you run it a second time:
var firstRandomChoice = array.splice(Math.floor(Math.random()*array.length), 1);
var secondRandomChoice = array.splice(Math.floor(Math.random()*array.length), 1);
If you use a utility library such as lodash, you may already have a function available to do this for you. For example, lodash provides sample(). So if you were using lodash, you could just do something like this to get an array of two random items:
var results = _.sample(array, 2);
Related
This question already has answers here:
How can I remove a specific item from an array in JavaScript?
(142 answers)
How to remove item from array by value? [duplicate]
(37 answers)
Closed 2 months ago.
I have an array which has some empty items.
const array = ["a","","c","","e","f","g"]
I am trying to eliminate empty items and leave only the items having string. I mean manipulating the array as:
array = ["a","c","e","f","g"]
There are many alternative like array.map, array.filter, array.slice, array.splice.. What is the most costless and recommended way of doing this?
As far as I know most cost effective way is to use the array filter method:
const array = ["a","","c","","e","f","g"];
const results = array.filter(element => {
return element !== '';
});
console.log(results);
This question already has answers here:
Why Array.indexOf doesn't find identical looking objects
(8 answers)
Closed 3 years ago.
I'm wondering what the best way to determine the membership of one array in another array in JS.
Here's an example
let a = [];
a.push([1,2]);
a.includes([1,2]) <- evaluates to false
a.indexOf([1,2]) <- evaluates to -1
What's the deal here? Any efficient work around?
At the moment, your search array doesn't actually equal the array within your a array as they have 2 different references in memory. However, you could convert your arrays to strings, such that your search can equal another string array within your array.
To do this you could convert your inner arrays to string using .map(JSON.stringify) and then search for the string version of your array using .includes(JSON.stringify(search_arrr)).
See example below:
let a = [];
let search = [1, 2];
a.push([1,2]);
a = a.map(JSON.stringify)
console.log(a.includes(JSON.stringify(search)));
This question already has answers here:
From an array of objects, extract value of a property as array
(24 answers)
Closed 3 years ago.
I have a JSON object in a JavaScript function:
[{"PMID":31206477,"MemberID":1287,"recID":6352},
{"PMID":31202264,"MemberID":1245,"recID":5974},
{"PMID":31201299,"MemberID":1184,"recID":3012},
{"PMID":31196160,"MemberID":1241,"recID":3833}]
That is saved to an Multi-dimensional Array
Is there a better way that I can make a make a new Array with only the PMID element without looping and building it. I know that this question is close to a duplicate but I'm not interested in a merge or a concat. Currently I'm doing
var newArray = [];
for (var i = 0; i < this.pmidList.length; i++) {
newArray.push(this.pmidList[i]["PMID"]);
}
This question maybe a duplicate but if the average person can't find it based upon the title then it should not be considered a duplicate. The solution is the same but the question titles are much different.
You can use the Array.map function.
const input = [{"PMID":31206477,"MemberID":1287,"recID":6352},
{"PMID":31202264,"MemberID":1245,"recID":5974},
{"PMID":31201299,"MemberID":1184,"recID":3012},
{"PMID":31196160,"MemberID":1241,"recID":3833}];
const output = input.map(item => item.PMID);
Documentation
This question already has answers here:
How can I create a two dimensional array in JavaScript?
(56 answers)
Closed 5 years ago.
I am creating a map of array using this:
var m = new Map(Array(40).fill(new Array()).entries());
Now, I want to push values in those array. But when I do this:
m.get(1).push(10)
The value 10 gets pushed into all the arrays instead of the one at 1st position.
You could take another pattern to build independent arrays.
var m = new Map(Array.from({ length: 40 }, _=> []).entries());
m.get(1).push(10);
console.log([...m]);
fill gets single array an uses it to fill all rows of the given array, it doesn't create a new array for each row. This means that your single array reference is shared between all rows. Because array is a reference type, you use the single reference to manipulate it, so the actual object is changed. You can check this by comparing the references of each row.
const arr = new Array(2).fill(new Array());
console.log(arr[0] === arr[1]);
For creating separate arrays, you can see #Nina's answer above
This question already has answers here:
Sampling a random subset from an array
(15 answers)
Closed 8 years ago.
Say I had
var imgs = ["pItem1","pItem2","pItem3","pItem4","pItem5"]
How can get a new array from the current one, that randomly picks lets say 3 items from the old array and puts it in a new array.
var newArray =["pItem1," "pItem4," "pItem2"];
You're basically looking to take a randomly sampled subset of an array. One approach is to randomly shuffle the array, then take a slice from the beginning of the array. See this implementation of getRandomSubarray() in another answer: https://stackoverflow.com/a/11935263/2943575