Javascript printing from nested arrays

Question

I am currently working on a random number generator script that will generate three numbers. The first two numbers will be used to pick a "cell" in a "table" by referencing the row and column. Within each cell are two numbers to choose from. The third number will then determine which of the two numbers to select. I have figured out most of this but I am having problems with the last part.

My "solution" was to create twenty arrays, and within each array are twenty more arrays. Here is an example of the first array:

In the header I have the following:

Scripts to generate the first two numbers:

var randOne20 = Math.floor(Math.random()*20);
var randTwo20 = Math.floor(Math.random()*20);

Here is the first row of the 20 arrays:

var lvl1Roll1 = [[ 1,0 ],[ 1,1 ],[ 1,2 ],[ 1,3 ],[ 1,4 ],[ 1,5 ],[ 1,6 ],[ 1,7 ],[ 1,8 ],[ 1,9 ],[ 1,10 ],[ 1,11 ],[ 1,12 ],[ 1,13 ],[ 1,14 ],[ 1,15 ],[ 1,16 ],[ 1,17 ],[ 1,18 ],[ 1,19 ]];

The second row would be "lvl1Roll2" and the third would be "lvl1Roll3" etc. all the way up to "lvl1Roll20."

In the body I have the following script:

var randOne = randOne20 + 1;

document.write(window['lvl1Roll'+randOne][randTwo20]);

The randOne variable is used to select the appropriate row.

I can figure out how to select a specific cell (using the randTwo20 variable) but I have no idea how to then select the first or the second number within each cell.

Now, just to clarify, I have not listed the third random number generator code because at the moment I am just trying to figure out how to select either the first or second number within each cell. Once I figure that out I can just use an if/else statement.

Also, if I did not want to print out the number but select it as a variable how would I do that?

Thank you for any and all help!

Take care and have a great day....

ciao, john.

How about just add yet another bracketed index to the expression? — Pointy
– Pointy, Commented Jan 17, 2012 at 0:18

Peter-Paul van Gemerden · Accepted Answer · 2012-01-17 01:31:20Z

I'm really not sure what you're trying to do, but... Getting the first of second element of an array is as simple as arr[0] and arr[1], like so:

// First:
document.write(window['lvl1Roll'+randOne][randTwo20][0]);

// Second:
document.write(window['lvl1Roll'+randOne][randTwo20][1]);

To randomize, just follow the same pattern as before, but use Math.round instead of Math.floor and don't multiply by 20:

var randOne20 = Math.floor(Math.random()*20);
var randTwo20 = Math.floor(Math.random()*20);
var randOne = Math.round(Math.random());

document.write(window['lvl1Roll'+randOne20][randTwo20][randOne]);

One more thing, though: you don't need to put the different rows in separate variable. You can just make it one big array:

var lvl1Roll = [
    [
        [ 1,0 ], [ 1,1 ], [ 1,2 ], [ 1,3 ], [ 1,4 ], [ 1,5 ], [ 1,6 ], [ 1,7 ], [ 1,8 ], [ 1,9 ], [ 1,10 ], [ 1,11 ], [ 1,12 ], [ 1,13 ], [ 1,14 ], [ 1,15 ], [ 1,16 ], [ 1,17 ], [ 1,18 ], [ 1,19 ]
    ],
    // [ lvl1Roll2 ],
    // [ lvl1Roll3 ], etc.
];

And use then use this to select a value from the table and put it into the variable result:

var result = lvl1Roll[randOne20][randTwo20][randOne];

And finally: I suspect that, I you were to tell us the logic behind the "rolls", it's quite plausible that you don't need this "table" at all. I could be wrong, but... might it be worth posting another question about that? Just a thought.

Thank you everyone for you replies. PPvG, arr[0]/arr[1] is exactly what I was looking for. I must have had a massive brain fart because I thought I tried that and did not get the result I was looking for. I just tried it and it worked fine. Thanks! In regards to the random function, I should have mentioned that I am generating a random number between 1 and 20.
(Perhaps you tried [1] and [2]?) Call me daft, but... doesn't 1 + Math.floor(Math.random()*20) do exactly what you need? It generates a random number between 1 and 20 (inclusive).

RobG · Accepted Answer · 2012-01-17 00:26:47Z

0

If you want a random choice between two numbers (assuming 0 and 1), then:

var i = Math.random() < 0.5? 0 : 1;

or

var i = Math.random()*2 | 0;

should do the job. So:

document.write(window['lvl1Roll'+randOne][randTwo20][i]);

or

document.write(window['lvl1Roll'+randOne][randTwo20][Math.random() < 0.5? 0 : 1]);

or

document.write(window['lvl1Roll'+randOne][randTwo20][Math.random()*2 | 0);

How many do you want? :-)

edited Jan 17, 2012 at 0:26

answered Jan 17, 2012 at 0:20

RobG

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1 Comment

Peter-Paul van Gemerden Over a year ago

Or just Math.round(Math.random())

pseudosavant · Accepted Answer · 2012-01-17 00:55:05Z

If I understand you correctly I think the easiest way to do this would be with one array that contained multiple arrays. The first would be the table array, each entry in the table array would be a row and each entry in a row would be a cell. This would make it really easy to reference any cell in the table. Here is a 3x3 example:

var table = [
    [0,1,2],
    [3,4,5],
    [6,7,8],
];

table[0][0]; // First Row, First Column, Equals 0;
table[1][1]; // Second Row, Second Column, Equals 4;
table[2][2]; // Third Row, Third Column, Equals 8;

You could actually push your 20 arrays into an array to create the table if you'd like:

var table = [];
table.push(randOne20);
table.push(randTwo20);
etc...

If you want to automatically load the arrays with random numbers you could easily do that with a loop.

var table = [];
for (var i = 0; i < 20; i++){ // Create 20 rows
    var row = [];
    for (var x=0; i<20; i++){ // Create 20 cells;
        var cell = [Math.round(Math.random), Math.round(Math.random)]; // Adds a two item array of random 0's or 1's
        row.push(cell); // Adds the cell to the row
    }
    table.push(row); // Adds the row to table
}

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