I have an array of objects like this:
[
{ name: "Group 1", value: "Foo" },
{ name: "Group 2", value: "Bar" },
{ name: "Group 1", value: "Baz" }
]
I'd like to use Partial Lenses library to transform these groups to keys of an object with corresponding group's items, like this:
{
"Group 1": [
{ name: "Group 1", value: "Foo" },
{ name: "Group 1", value: "Baz" }
],
"Group 2": [
{ name: "Group 2", value: "Bar" }
]
}
My current approach is like this, assuming I have the source data in a variable called data
:
const grouped = L.collect([L.groupBy('name'), L.entries], data)
const setKey = [L.elems, 0]
const getName = [L.elems, 1, 0, 'name']
const correctPairs = L.disperse(setKey, L.collectTotal(getName, grouped), grouped)
L.get(L.inverse(L.keyed), correctPairs)
I don't like that I need to use the grouped
and correctPairs
variables to hold data, as I probably should be able to do the transformation directly in the composition. Could you help me to compose the same functionality in a more meaningful way?
Here's a Partial Lenses Playground with the above code.
I assume the goal is to actually create an isomorphism through which one can
view such an array as an object of arrays and also perform updates. Like a
bidirectional version of e.g. Ramda's
R.groupBy
function.
Indeed, one approach would be to just use Ramda's
R.groupBy
to implement a new primitive
isomorphism using L.iso
.
Something like this:
const objectBy = keyL => L.iso(
R.cond([[R.is(Array), R.groupBy(L.get(keyL))]]),
R.cond([[R.is(Object), L.collect([L.values, L.elems])]])
)
The conditionals are needed to allow for the possibility that the data is not of
the expected type and to map the result to undefined
in case it isn't.
Here is a playground with the above Ramda based
objectBy
implementation.
Using only the current version of Partial Lenses, one way to compose a similar
objectBy
combinator would be as follows:
const objectBy = keyL => [
L.groupBy(keyL),
L.array(L.unzipWith1(L.iso(x => [L.get(keyL, x), x], L.get(1)))),
L.inverse(L.keyed)
]
Perhaps the interesting part in the above is the middle part that converts an
array of arrays into an array of key-array pairs (or the other way around).
L.unzipWith1
checks that all the keys within a group match, and if they don't, that group
will be mapped to undefined
and filtered out by
L.array
. If desired,
it is possible to get stricter behaviour by using
L.arrays
.
Here is a playground with the above composed
objectBy
implementation.