Crossfilter and DC.js: reduce to unique number

Question

In the example below, I am trying to sum by unique occurence of Respond_Id. eg. in this case, it should be in total 3, "Respond_Id" being 258,261 and 345.

This is my data:

{"Respond_Id":258,"Gender":"Female","Age":"18-21","Answer":424},
{"Respond_Id":258,"Gender":"Female","Age":"18-21","Answer":428},
{"Respond_Id":261,"Gender":"Male","Age":"22-26", "Answer":427},
{"Respond_Id":261,"Gender":"Male","Age":"22-26",  "Answer":432},
{"Respond_Id":345,"Gender":"Female","Age":"27-30","Answer":424},
{"Respond_Id":345,"Gender":"Female","Age":"27-30","Answer":425},
{"Respond_Id":345,"Gender":"Female","Age":"27-30","Answer":433},

I know I should use group reduce for this, so I tried (adapted from an example):

var ntotal =  answerDim.group().reduce(
                function(p, d) { 
                    if(d.Respond_Id in p.Respond_Ids){
                        p.Respond_Ids[d.Respond_Id]++;
                    }
                    else {
                        p.Respond_Ids[d.Respond_Id] = 1;
                        p.RespondCount++;
                    }
                    return p;
                },
                function (p, d) {
                    p.Respond_Ids[d.Respond_Id]--;
                    if(p.Respond_Ids[d.Respond_Id] === 0){
                        delete p.Respond_Ids[d.Respond_Id];
                        p.RespondCount--;
                    }
                    return p;
                },
                function () {
                    return {
                        RespondCount: 0,
                        Respond_Ids: {}
                    };

                }
            );

Then:

numberDisplay
         .group(ntotal)
         .valueAccessor(function(d){ return d.value.RespondCount; });

     dc.renderAll();

But seems not working. Does someone know how to make it work ? Thank you

It looks to me like this should basically work. What kind of error are you getting and can you please provide an example with full working code? If you don't want to fiddle with reducers yourself, you may also want to look at Reductio as an option: github.com/crossfilter/… — Ethan Jewett
Thank you for your answer. What I am getting when logging d in the valueAccessor is this: {"key":433,"value":{"RespondCount":1,"Respond_Ids":{"345":1}}} — road
You need to share a complete example with us. I would guess that your dimension definition and group definition are conflicting, but since you don't share your dimension definition, I can't really tell. — Ethan Jewett
Also (and sorry for the multiple comments), please share what you would expect/want to see. See here for further tips on examples in questions: stackoverflow.com/help/mcve — Ethan Jewett
Thanks for the replies. The result I would like to have is the total number of respondant based on their Respond_id. In the example above it should be 3. Here is a fiddle of my code . jsfiddle.net/wa9oxsdg/6. Thank you ! — road

Ethan Jewett Ethan Jewett · Accepted Answer · 2017-07-31T16:26:16

Based on your JSFiddle, your setup is like this:

var RespondDim       =  ndx.dimension(function (d) { return d.Respond_Id;});
var ntotal           =  RespondDim.group().reduce(
                                function(p, d) { 
                                    if(d.Respond_Id in p.Respond_Ids){
                                        p.Respond_Ids[d.Respond_Id]++;
                                    }
                                    else {
                                        p.Respond_Ids[d.Respond_Id] = 1;
                                        p.RespondCount++;
                                    }
                                    return p;
                                },
                                function (p, d) {
                                    p.Respond_Ids[d.Respond_Id]--;
                                    if(p.Respond_Ids[d.Respond_Id] === 0){
                                        delete p.Respond_Ids[d.Respond_Id];
                                        p.RespondCount--;
                                    }
                                    return p;
                                },
                                function () {
                                    return {
                                        RespondCount: 0,
                                        Respond_Ids: {}
                                    };
                                 });

What is important to note here is that your group keys, by default, are the same as your dimension keys. So you will have one group per respondent ID. This isn't what you want.

You could switch to using dimension.groupAll, which is designed for this use case, but unfortunately the dimension.groupAll.reduce signature is slightly different. The easiest fix for you is going to be to just define your dimension to have a single value:

var RespondDim       =  ndx.dimension(function (d) { return true;});

Now you'll see that ntotal.all() will look like this:

{key: true, value: {RespondCount: 3, Respond_Ids: {258: 2, 261: 2, 345: 3}}}

Working fiddle: https://jsfiddle.net/v0rdoyrt/2/

Crossfilter and DC.js: reduce to unique number

1 Answers