Performing cartesian product, intersection and except over two arrays

The helper $from simplifies the handling of an array of maps but it can also help performing functions with other arrays of maps namely for a cartesian product, intersection and except operations.

Defining two sets of values

Let’s start be defining two arrays of maps. A first set of values composed of maps with a x value and a y value:

var a = [
    { x: 1, y: -1 },
    { x: 2, y: -1 }
]

And a second set of values where one entry is also present on the first set of values:

var b = [
    { x: 1, y: 1 },
    { x: 2, y: 2 },
    { x: 2, y: -1 }
]

You can check the size of each (#2 for a and #3 for b):

tprint("size of a = {{sizeA}} | size of b = {{sizeB}}", { sizeA: $from(a).count(), sizeB: $from(b).count() })

Performing an intersection

To perform a intersection between a and b simply execute:

var c = $from(a).intersect(b).select()

The result will be a new set c with 1 element (x: 2 and y: -1):

printTable(c)

Performing an exception

To obtain the exception between a and b simple execute:

var c = $from(a).except(b).select()

The result will be 1 element (excluding the common element between a and b):

printTable(c)

Performing a cartersian product

A cartesian product between one set and another set will combine each element of the first set with all elements of other set. To better visualize let’s create a third set z:

var z = [
    { z: 1 },
    { z: -1 }
]

Now let’s execute the cartesian product between a and z:

var c = $from(a).cartesian(z).select()

The result will be a new set c with 4 elements:

x	y	z
1	-1	1
1	-1	-1
2	-1	1
2	-1	-1

printTable(c)