How to find the row and column of a specific element in a multidimensional array using javascript

Question

I have this array 8x8 array which is supposed to represent a checkerboard.

 var board = [['RS', 'H',  'RS', 'H',  'RS', 'H',  'RS', 'H'],
          ['BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS'],
          ['RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS'],
          ['BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS'],
          ['RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS'],
          ['BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS'],
          ['RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS'],
          ['F', ' RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS']
 ];

I want to get the element F's row and column number I am trying to use a 4 loop

 function getF(board) {
    var i, j;
    for (i = 0; i < 8; i++) {
      for (j = 0; j < 8; j++) {
        if(board[i][j] == 'F'{

     return {row:1, col:j};

How do I do this to get the indexes of all H elements?

you need some array to store the result, each element is an object like {row: x, col: y} — King King
– King King, Commented Oct 14, 2014 at 17:48
Your question is unclear, do you want to find the location of F or are you trying to locate all H entries? — SnowInferno
– SnowInferno, Commented Oct 14, 2014 at 17:49

thecodeparadox · Accepted Answer · 2014-10-14 18:10:31Z

1

You can simplify your function like:

 function getCharIndexes(board, char) {
    var i, j, collection = [];
    for (i = 0; i < board.length; i++) {
      for (j = 0; j < board[i].length; j++) {
        if(board[i][j] == char) {
            collection.push({row:1, col:j}); // should be {row: i, col: j}
        }
      }
    }
    return collection;
  }

To get 'F' call: getCharIndexes(board, 'F');

To get 'H' call: getCharIndexes(board, 'H');

etc.

edited Oct 14, 2014 at 18:10

answered Oct 14, 2014 at 17:52

thecodeparadox

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4 Comments

Rafael Eyng Over a year ago

This will not return what you want, since it is returning a position object with a fixed row of 1 for every match of the char parameter. It should be collection.push({row:i, col:j}) instead

King King Over a year ago

@RafaelEyng yes, I doubt it's the problem of copying the OP's code, 1 here should be i.

thecodeparadox Over a year ago

@RafaelEyng Hi, yes I just copy from OP's code, but now I added comment also.

George C Ulloa Over a year ago

How can I compare the rows and columns from H and F?

Flynn · Accepted Answer · 2014-10-14 17:52:37Z

0

First, you are missing your closures for your if statement and for loops, I assume that this is a copy/paste issue.

Next, I don't think your getF function is working, because you are returning the column as j, but the row is always 1. To fix that, just return { row: i, col: j } instead.

Finally, the you can use the same loop operation to get all the 'H's, but just keep them in an array, and as you find them, append them using something similar to: foo.push({ row: i, col: j });

answered Oct 14, 2014 at 17:52

Flynn

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Comments

Martijn · Accepted Answer · 2014-10-14 17:58:54Z

0

The other answers are almost right:

var board = [['RS', 'H',  'RS', 'H',  'RS', 'H',  'RS', 'H'],
    ['BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS'],
    ['RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS'],
    ['BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS'],
    ['RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS'],
    ['BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS'],
    ['RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS', 'BS'],
    ['F', ' RS', 'BS', 'RS', 'BS', 'RS', 'BS', 'RS']];

function getChar(board, c) {
    var i, j, collection = [];
    for (i = 0; i < board.length; i++) {
      for (j = 0; j < board[i].length; j++) {
        if(board[i][j] == c)
            collection.push({row:i, col:j});
      }
    }
    return collection;
}

console.log(getChar(board, "F"));
console.log(getChar(board, "H"));

answered Oct 14, 2014 at 17:58

Martijn

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2 Comments

George C Ulloa Over a year ago

How can I compare the rows and columns from H and F? This way I can see if the H should be a specific distance away from the F? For example it must be one row up and one row to the left of the fox?

Martijn Over a year ago

@GeorgeCUlloa F is always in 1 position?

Rafael Eyng · Accepted Answer · 2014-10-14 18:01:52Z

There are some syntax errors in your code. Besides that, this will do:

 function getIndexesOf(matrix, obj) {
    var i, j;
    var ret = []
    for (i = 0; i < matrix.length; i++) {
      var line = matrix[i];
      for (j = 0; j < line.length; j++) {
        if(board[i][j] == obj) {
          ret.push({row: i, col: j})
        }
      }
    }
    return ret;
  }

This way, you can call it passing what object you want to find (as your 'H'):

getIndexesOf(board, 'H');

Note that:

you are using literal values in your for loops. It would be better to use the length of the matrix and of the lines that you pass in.
in your example you are returning {row:1, col:j}. That is not correct, not even for your purposes in the example. In that case you would return {row:i, col:j}, because i holds the row number, and doesn't make sense to return a fixed row number of 1.

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