Porting a ruby method to javascript

Question

I am trying to port some ruby code to javascript but am struggling with one particular line

The Ruby code is below: It removes all the full rows from a game of tetris:

  # removes all filled rows and replaces them with empty ones, dropping all rows
  # above them down each time a row is removed and increasing the score.  
  def remove_filled
    (2..(@grid.size-1)).each{|num| row = @grid.slice(num);
      # see if this row is full (has no nil)
      if @grid[num].all?
        # remove from canvas blocks in full row
        (0..(num_columns-1)).each{|index|
          @grid[num][index].remove;
          @grid[num][index] = nil
        }
        # move down all rows above and move their blocks on the canvas
        ((@grid.size - num + 1)..(@grid.size)).each{|num2|
          @grid[@grid.size - num2].each{|rect| rect && rect.move(0, block_size)};

          # I can't port this line
          @grid[@grid.size-num2+1] = Array.new(@grid[@grid.size - num2])
        }
        # insert new blank row at top
        @grid[0] = Array.new(num_columns);
        # adjust score for full flow
        @score += 10;
      end
    }
    self
  end

where @grid is a 2 dimensional array, initialised as follows:

@grid = Array.new(num_rows) {Array.new(num_columns)}

the javascript I have done so far is below

I have noted in the comment which is the line I can't work out

removeFilled() {
            for (var i = 2; i < this.grid.length; i++) {
                var row = this.grid.slice(i);

                var allFull = true;

                for (var g = 0; g < this.grid[i].length; g++ ) {
                    if (this.grid[i][g] == undefined) {
                        allFull = false;
                        break;
                    }
                }

                if (allFull) {
                    for (var j = 0; j < this.numColumns; j++) {
                        this.grid[i][j].remove();
                        this.grid[i][j] = undefined;
                    }

                    for (var k = this.grid.length - i + 1; k <= this.grid.length; k++) {

                        var rects = this.grid[this.grid.length - k];

                        for(var l = 0; l < rects.length; l++) {
                            var rect  = rects[l];
                            if (rect) {
                                rect.move(0, this.blockSize);
                            }
                        }

                        // ***this is the line I can't port
                        this.grid[this.grid.length - k + 1] = new Array(this.grid[this.grid.length - k]);
                    }

                    this.grid[0] =  new Array(this.numColumns);
                    this.score += 10;
                }
            }
        }

any ideas how to port the line in question?

Well, why can't you port it? (You probably want to look at Array.slice.) — Paul
– Paul, Commented Jul 4, 2013 at 21:57
so start with: grid[grid.length - k + 1] = grid[grid.length - k]. Okay, we're getting somewhere. So what does Array.new(arr) in ruby do? — Paul
– Paul, Commented Jul 4, 2013 at 22:10
Does this.grid[this.grid.length - k + 1] exist or is it being created? If it's being created then this.grid.length will increase by one and thus this.grid[this.grid.length - k] is actually itself! Unless this is the intention you should set it to a variable and use that instead: var currentGridLenght = this.grid.length; — Moob
– Moob, Commented Jul 4, 2013 at 22:38
yes, it exists. It is a row in the 2D grid. it needs to be initialised with whatever the code on right hand side of the equals sign is doing (in the Ruby code ). — ChrisCa
– ChrisCa, Commented Jul 4, 2013 at 22:52
Its setting the item in the grid array to be the same as the item before it (thus moving it down). Something like row[3] = a copy of row[2]. Doesn't seem entirely logical but i'm not familiar with Ruby. In javascript I would add an item at the top of the array .unshift() and .pop() the last one off the end (thus moving them down one). — Moob
– Moob, Commented Jul 4, 2013 at 23:23

raam86 · Accepted Answer · 2013-07-04 23:35:17Z

1

If I understand correctly you want to take the array in a given position and copy it one position forward.

You can do this:

  this.grid[this.grid.length - k + 1] =  this.grid[this.grid.length - k].slice(0);

answered Jul 4, 2013 at 23:35

raam86

6,8812 gold badges33 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

ixti · Accepted Answer · 2013-07-05 01:41:41Z

1

TL;DR @raam86 gave a correct answer. Difference is that in ruby Array.new old_arr will create a copy of array. In JS you achieve same with old_arr.slice()

As far as I understand your snippet can become something like this:

function falsy(val) {
  return undefined === val || null === val || false === val;
}

function all(arr) {
  return arr.reduce(function (a, b) { return a && !falsy(b); }, true);
}

// removes all filled rows and replaces them with empty ones, dropping all rows
// above them down each time a row is removed and increasing the score.
function removeFilled() {
  var i, j, k, rects,
      _grid       = this.grid,
      _numColumns = this.numColumns,
      _blockSize  = this.blockSize;

  for (i = 2; i < _grid.length; i++) {
    // see if this row is full (has no nil)
    if (all(_grid[i])) {
      // remove from canvas blocks in full row
      for (j = 0; j < _numColumns; j++) {
        _grid[i][j].remove();
        _grid[i][j] = undefined;
      }

      // move down all rows above and move their blocks on the canvas
      for (j = _grid.length - i + 1; j < _grid.length; j++) {
        rects = _grid[_grid.length - j];
        for (k = 0; k < rects.length; k++) {
          if (!falsy(rects[k])) {
            rects[k].move(0, _blockSize);
          }
        }

        _grid[_grid.length - j + 1] = _grid[_grid.length - j].slice();
      }

      _grid[0] = new Array(_numColumns);
      this.score += 10;
    }
  }

  return this;
}

PS You should really review the logic you are using and consider refactor it. For example in one place you use num_columns in another you relay on row's amount of elements. You iterate though array changing it, I recommend you consider manipulating on a copy of array in this case your code will become less complex.

answered Jul 5, 2013 at 1:41

ixti

1542 silver badges5 bronze badges

2 Comments

ChrisCa Over a year ago

thanks - I agree. Once I have a working copy I inrend to heavily refactor it. I will probably use underscore js for a lot of this.

ixti Over a year ago

I recommend you consider lodash instead of underscore. Or even go with Sugar.js for more ruby-ness :D

Collectives™ on Stack Overflow

Porting a ruby method to javascript

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related