Functional approach of removing items in a list based on nested property values

Question

I am trying move more towards functional programming in my javascript applications. I currently use the library ramda as a base lib for this.

My desire:

Create a function removeUserFromList(username, list) which returns the items in the list that does not match the username.
Make the implementation as short as possible, relying on existing functions in the Ramda library as much as possible.

Conditions:

A list containing nested user objects:

[{
    providers: {
        github: {
            login: "username1"
        }
    }

},
{
    providers: {
        github: {
            login: "username2"
        }
    }

}]

Acheived so far:

var list = [{providers: {github: {login: "username1"}}},
            {providers: {github: {login: "username2"}}}];

var getLoginName = R.useWith(R.path('providers.github.login'));
var isLoginNameEq = R.useWith(R.eq, getLoginName);

isLoginNameEq(list[0], "username1") // => true

//From this point on I am totally clueless, 
//but I believe I should combine these functions 
//with R.reject in some way.

Plunkr demo:

http://plnkr.co/edit/1b5FjxV3Tcgz7kozW1jX

Question:

Is there any better suited function to achieve something similar to R.eq but on nested objects (perhaps R.pathEq)?

score 6 · Accepted Answer · edited Sep 15 '19 at 17:21

I just got a pull request for R.pathEq merged. It won't be usable until the next release of ramda.js (current version is 0.6.0) but meanwhile you can recreate it like this:

var pathEq = R.curry(function(path, val, obj) {
    return R.eq(val, R.path(path, obj));
});

And then use it like so:

 var rejectThis = 'userName1';
 var myFilter = R.useWith(R.reject, pathEq('providers.github.login'):
 var filteredList = myFilter(rejectThis, users);

score 1 · Answer 2 · answered Oct 12 '14 at 00:10

Extending the solution from @LudwigMagnusson, a bit, you could do this:

// terrible name, but I'm never good at that.
var rejectPathVal = R.curry(function(path, val, list) {
    return R.reject(R.pathEq(path, val), list);
});

var filteredList = rejectPathVal('providers.github.login', 'userName1', list);

And of course you could then use it like:

var myFilter = rejectPathVal('providers.github.login', 'userName1');
// ...
var filteredList = myFilter(list);

or in any way you choose, given that it's fully curried. Although as Ludwig pointed out, pathEq is not in the released version of Ramda, you can get it by downloading the HEAD version from Github, or you could use the version Ludwig supplied above.

But I want to question your requirements a bit. I applaud your attempt to move to a more functional style. I'm one of the authors of Ramda, and think it's a great choice for a library, but this seems to be unnecessary:

Make the implementation as short as possible, relying on existing functions in the Ramda library as much as possible.

I would suggest that goals of readability should always trump goals of terseness. Granted, elegance and readability are often tied together with brevity, but "as short as possible" should never be a driving goal.

Thanks, I'll keep in mind that readability > terseness the next time. It's just so fun writing shorter programs. :) Btw. great work with Ramda. — horte, Oct 16 '14 at 09:16

score 1 · Answer 3 · answered Oct 13 '14 at 12:32

if you don't need to create the function point-free, you can simply:

var removeUserFromList= function(name, list) {
    return R.reject(pathEq('providers.github.login', name), list);
}
console.log(removeUserFromList('username1', users));

using @Ludwig Magnussen's pathEq function.

Functional approach of removing items in a list based on nested property values

3 Answers3