Updating an object within an array using Mongo and Meteor

Question

Within my Meteor application, I have a document (from the mongo collection) for which a portion of the data within it is an array of objects.

I have created a loop that goes through the array of objects, uses information from the object within each array index to calculate new data points. (specifically, using a mean to calculate variance and standard deviation).

I then want to update the object, at that array index, to include the new data points (variance and standard deviation).

JSON object:

    "row_sum" : [
    {
        "name" : "Total Inches of Rainfall",
        "row_int" : 1,
        "mean" : 14.492753623188406
    },
    {
        "name" : "Inches Above/Below (+/-)135 Year Average",
        "row_int" : 2,
        "mean" : 0.13043478260869565
    }
],

My desired output is:

    "row_sum" : [
    {
        "name" : "Total Inches of Rainfall",
        "row_int" : 1,
        "mean" : 14.492753623188406
        "variance" : 1234,
        "sd" : 1111
    },
    {
        "name" : "Inches Above/Below (+/-)135 Year Average",
        "row_int" : 2,
        "mean" : 0.13043478260869565,
        "variance" : 1234,
        "sd" : 1111
    }
],

Here's my current output:

    "row_sum" : [
    {
        "name" : "Total Inches of Rainfall",
        "row_int" : 1,
        "mean" : 14.492753623188406
    },
    {
        "name" : "Inches Above/Below (+/-)135 Year Average",
        "row_int" : 2,
        "mean" : 0.13043478260869565
    },
    {
        "variance" : 48.24328113588513,
        "sd" : 6.945738343465375
    },
    {
        "variance" : 48.024652540384196,
        "sd" : 6.929982145747866
    }
],

As you can see, it's simply appending the data as a new object within the array of objects, rather than updating the specific object indexed within the array's loop.

Here's the section of code that contains the loop and the Mongo Update command:

for (var i = 0; i < row_sum.length; i++){
        var variance = this.calculate_variance(data_summary_id, row_sum[i]);    
        var standard_deviation = Math.sqrt(variance);
         var sum_data = {
                    row_sum : { 
                        variance: variance,
                        sd: standard_deviation
                }
            }
        DataSetSummary.update(data_summary_id, {$push: sum_data});

    }

score 1 · Answer 1 · edited May 23 '17 at 10:26

1

Try $set method and positional operator $ . Use the following query

db.test.update({"row_sum.row_int":1},{$set:"row_sum.$.variance":1,"row_sum.$.sd" : 6.9}})

Since it is an element in row you will have to use positional arguments try the following question for more answer

edited May 23 '17 at 10:26

Community

1
1

answered Mar 04 '15 at 07:18

The6thSense

8,103
8
31
65

1

You cannot use the positional operator with `upsert` and that option really would not be needed in this context since it is updating existing array elements. You would also need the master document `_id` value as part of the query since this is all about updating one document and indeed one array element per update. Otherwise the basic principle is correct. – Neil Lunn Mar 04 '15 at 07:28
This would be really nice if you could add some JavaScript code as an example of how to construct and execute that based on the code already given in the question. Might even get you some more upvotes for such a useful example :) – Neil Lunn Mar 04 '15 at 10:40
Sorry bro don't know java script that much – The6thSense Mar 04 '15 at 11:09

Updating an object within an array using Mongo and Meteor

1 Answers1