dataTable should probably not use .top(), .bottom()

Hi, I’m trying to implement data table(car model name and speed) and select menu (Day- monday and so). Link to the demo site my json data here is my code for data table

var car =  dc.dataTable('#car')
                .dimension(carGrpdDim)
                .group(function (d){ return 'Modal | Speed'})
                .columns([function (d) { return d.key },  function (d) { return d.value.total }])
                .sortBy(function (d) { return d.value.total })
                .order(d3.descending)
                .size(5)

select menu code

var day = dc.selectMenu('#day')
            .dimension(dayDim)
            .group(dayGrp)
            .controlsUseVisibility(true)
                .promptText('Day');
            day.title(function (d) {
                return d.key;
            });

i want to show only top 5 cars for the day. So i added size(5) but I’m getting cars with speed 0. Though I have cars with speed greater than 0.

Thanks.

[gordonwoodhull]

Thanks for including a reproducible example! The issue here is that the data table uses dimension.top(N) to determine which rows to show when dataTable.size() is enabled.

Since you are using a group for your dimension, that resolves to group.top(N), which

Returns a new array containing the top k groups, according to the group order of the associated reduce value. The returned array is in descending order by reduce value.

The “group order” is determined by group.order(f), and by default that attempts to use the reduced values directly for ordering. This won’t work in your case because the reduced values are objects. I guess this somehow results in a no-op, so you get the first five in alphabetical ordering based on the key.

You can fix your example by specifying group.order():

       carGrpdDim.order(v => v.total);

Demo fiddle: https://jsfiddle.net/gordonwoodhull/cbyktand/10/

The use of .top() is documented quite a few places in the dataTable documentation, however it’s pretty confusing. I don’t think it would be a huge performance hit to just take top(Infinity), then sort and cap, as we are already doing in the capped charts (pie, row) per #934.

I’ll retitle this issue accordingly. It’s a little tricky to do in a backward compatible way, but we mostly succeeded for the capped charts.

[vikkya]

Thanks @gordonwoodhull . It solved the issue.