pulling a random item from multiple arrays

Question

I have 12 arrays named f1 to f12 each with five items. I want to randomly pull one item from each array and push these into the new array sm1.

var sm1 = [];

for (var i=1; i<=12; i++) {
    randomPrompt = Math.floor((Math.random() * 5));
    sm1.push("f"+i[randomPrompt]);
}

However, this returns a random index of "f"+i instead of it indexing f1, f2, f3, f4, etc.

Any time you find yourself creating numeric variables like that, you should be using an array instead. — Barmar
– Barmar, Commented Jun 4, 2017 at 6:12
thanks for the reminder. Yes, in this case, the f1 to f12 variable names are specific to the context I'm working in and cross-reference curriculum content. Using them will allow non-coders who have to tweak this to know which bits to tweak. — Mikawa Ben
– Mikawa Ben, Commented Jun 4, 2017 at 6:28

Nikhil Rajawat · Accepted Answer · 2017-06-04 05:56:34Z

3

Why don't you use a 2-d array instead of 12 single arrays. Then it will be very easy.

answered Jun 4, 2017 at 5:56

Nikhil Rajawat

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Comments

Jaspreet Singh · Accepted Answer · 2017-06-04 06:10:00Z

1

Changes below line

sm1.push("f"+i[randomPrompt]);

to

sm1.push(eval("f"+i+"["+randomPrompt+"]"));

answered Jun 4, 2017 at 6:10

Jaspreet Singh

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Comments

Ali Hesari · Accepted Answer · 2017-06-04 06:27:15Z

0

There's a few ways to accomplish what you ask.

Example:

var myArray = {
   "f1": [1,2,3,4,5],
   "f2": [6,7,8,9,10],
   "f3": [11,12,13,14,15],
   "f4": [16,17,18,19,20]
}

var sm1 = [];
for (var i=1; i<=4; i++) {
    randomPrompt = Math.floor((Math.random() * 5));
    sm1.push(myArray["f"+i][randomPrompt]);
}
console.log(sm1);

OR, If you are using code in the browser:

f1 = [1,2,3,4,5];
f2 = [6,7,8,9,10];
f3 = [11,12,13,14,15];
f4 = [16,17,18,19,20];

var sm1 = [];

for (var i=1; i<=4; i++) {
    randomPrompt = Math.floor((Math.random() * 5));
    sm1.push(window["f"+i][randomPrompt]);
}
console.log(sm1);

Or use eval():

f1 = [1,2,3,4,5];
f2 = [6,7,8,9,10];
f3 = [11,12,13,14,15];
f4 = [16,17,18,19,20];

var sm1 = [],item;

for (var i=1; i<=4; i++) {
    randomPrompt = Math.floor((Math.random() * 5));
    item = eval(["f"+i][0]);
    sm1.push(item[randomPrompt]);
}
console.log(sm1);

edited Jun 4, 2017 at 6:27

answered Jun 4, 2017 at 6:11

Ali Hesari

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1 Comment

Mikawa Ben Over a year ago

thanks Ali. Very comprehensive. Appreciate you adding different versions as it helps me see other approaches. The second worked fine and most closely followed the code I'm using.

Alexios Tsiaparas · Accepted Answer · 2017-06-04 06:01:38Z

0

You can use the window object.

var sm1 = [];

for (var i=1; i<=12; i++) {
    randomPrompt = Math.floor((Math.random() * 5));
    sm1.push(window["f"+i][randomPrompt]);
}

answered Jun 4, 2017 at 6:01

Alexios Tsiaparas

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2 Comments

Jaspreet Singh Over a year ago

You can 'this' or current scope in case it is not global.

Mikawa Ben Over a year ago

I'm actually working globally at this point in the code so this is appropriate. I appreciate your warning though @Barmar.

hirowaki · Accepted Answer · 2017-06-04 07:48:41Z

0

var sm1 = [f1, f2, f3, f4, f5, f6, f7, f8, f9, f10, f11, f12].map(function (arr) {
    return arr[Math.floor((Math.random() * arr.length))];   
});

I'd vote using 2-d array instead of named 12 single arrays though.

answered Jun 4, 2017 at 7:48

hirowaki

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