Creating new jinqJs instance for different queries on same base

Hi,

First of all thank you for such great lib, I really appreciate it.

The only drawback i found during usage is: Let's say i want to apply different "filters" on initially filtered data. jinqJs needs to be created and filtered on initial state for all of such types of cases.

ex: Let's say we have an array with 100 elements (rows), with date field inside.

First of all, I want to filter by month and assign it to some variable:

var year = 2017;
var month = 12;
var filtered_by_month = new jinqJs().from(DATA).where(function(row) {
    var date = row.date;
    return date.getFullYear() === year && date.getMonth() === month;
});

Now if i want to get for example: SUM and COUNT, at first glance it's easy, because:

var sum = filtered_by_month.sum('amount').select();
var count = filtered_by_month.sum('amount').select();

But, as it appears, after the first usage (when we did get sum) of jinqJs instance - filtered_by_month, jinqJs instance appears to be empty and second expression did not evaluate anything, it became null.

This happens not only in case of SUM or COUNT, If i apply some GROUPING to it, I can't apply other GROUPING on filtered_by_month instance.

For that, unusual reason, I am creating new jinqJs instances every time, with same initial filter, to get desired results at the end.

I wish i could query my data like this:

var year = 2017;
var month = 12;
var filtered_by_month = new jinqJs().from(DATA).where(function(row) {
    var date = row.date;
    return date.getFullYear() === year && date.getMonth() === month;
});

var sum = filtered_by_month.groupBy('user').sum('amount').select();
var count = filtered_by_month.groupBy('branch').count('amount').select();
...

Thanks for creating such a great library again :)

fordth / jinqJs

Creating new jinqJs instance for different queries on same base #29