DataView - calculate dynamic columns from a given column id.

[James Patrick-Evans]

I'm using a DataView object to only select specific columns from a DataTable and draw then on a chart. I want to be able to create new columns in the DataView that are functions of the values already in the DataView. So far i have managed to produce a cumulative number from the code below (copy into google playground https://code.google.com/apis/ajax/playground/?type=visualization#table) however i want to know the column id of the column created in the dataview/pass the column id as well as the row number. For example I ultimately want to be able to have this:

|   Number 1   |    Number 2   |   Cumulative Number 1   |   Cumulative Number 2   |   Other functions

|        4          |           3        |                 4                   |                   3                |

|        2          |           1        |                 6                   |                   4                |

|        1          |           4        |                 7                   |                   8                |

|        0          |           2        |                 7                   |                  10                |

|        3          |           1        |                 10                 |                  11                |

|        5          |           0        |                 15                 |                  11                |

  // Create and populate the data table.
  var data = google.visualization.arrayToDataTable([
    ['Name', 'Foo Distance', 'Bar Distance', 'Smokes'],
    ['Tong Ning mu', 4, 3,  true],
    ['Huang Ang fa', 2, 6, false],
    ['Huang Ang fa', 1, 0, false],
    ['Huang Ang fa', 0, 2, false],
    ['Huang Ang fa', 3, 5, false],
    ['Huang Ang fa', 5, 7, false],
    ['Huang Ang fa', 8, 2, false],
    ['Huang Ang fa', 0, 1, false],
    ['Teng nu', 2, 0, true]
    
  ]);
  
  var dataview = new google.visualization.DataView(data);
    
  dataview.setColumns([1,2,{calc:cumulative, type:'number', label:'Foo :: Total Distance'}, {calc:cumulative, type:'number', label:'Bar :: Total Distance'}]);

 

function cumulative(dataTable, rowNum){
  if(rowNum > 0){
    return (dataview.getValue(rowNum-1, 2) + dataTable.getValue(rowNum, 1));
  }  
    return dataTable.getValue(rowNum, 1);
}
  // Create and draw the visualization.
  visualization = new google.visualization.Table(document.getElementById('table'));
  visualization.draw(dataview, null);
}
​

 function drawVisualization() {

The only way I could do this without column id is have a cumulative function for each column, however this needs to be dynamic.

tl;dr Basically i need a way to pass the column id into the calc function when calculating new columns.

 

i.e. 

 dataview.setColumns([1,2,{calc:cumulative(column_id_to_calc_cumulative_from), type:'number', label:'Foo :: Total Distance'}]);

[James Patrick-Evans]

Copying the playground code messed up, here's the full version: http://pastebin.com/q8Rxhut0

[asgallant]

There's no built-in way to use column ID's to get data from the DataTable (you have to parse the table to find the index of a column with the given ID; not difficult, but it is an extra step).  If your cumulative function can take a parameter for the column number, then you can use a method like this to create your calculated columns:

dataview.setColumns([1, 2, {
    calc: function (dt, row) {
        return sum(dt, row, 1);
    },

    type: 'number',
    label: 'Foo :: Total Distance'
}, {

    calc: function (dt, row) {
        return sum(dt, row, 2);
    },

    type: 'number',
    label: 'Bar :: Total Distance'
}]);

[James Patrick-Evans]

Thanks, that's exactly what i was looking for, ill try it out tomorrow.