Mapping edges to vertices with ramda

gistfile1.js

    var R = require('ramda');
    
    var list = ['a', 'b', 'c'];
    var edges = [[0, 1], [1,2]];
    var values;
    
    //1
    values = edges.map(function(edge) {
      return [ list[edge[0]], list[edge[1]] ];
    });

    //2
    values = edges.map(function(edge) {
      return edge.map(function(i) { return list[i]; });
    });

    //3
    values = R.map(function(edge) {
      return edge.map(function(i) { return list[i] });
    }, edges);

    //4
    values = R.map(function(edge) {
      return R.map(R.rPartial(R.prop, list), edge);
    }, edges);

    //5
    values = R.map(R.map(R.rPartial(R.prop, list)), edges);
    
    // Profit!
    // a) edge can have many indices and this still works
    // b) if list is a property than we can use `this.list` and don't worry as there is no nested functions
    // c) we need to change list variable in only one place
    // d) there is no edge variable at all
    // f) all that stuff is curried so:
    
    var listExtractor = R.map(R.map(R.rPartial(R.prop, list)));
    values = listExtractor(edges);
    values = listExtractor(anotherEdges);

cool! one teensy tweak makes it even shorter, and arguably more readable(?):

var listExtractor = R.map(R.map(R.props(list)));

An interesting way to extend this to make a two-argument function would be

var listExtractor = R.useWith(R.map, R.compose(R.map, R.props), R.identity);

Then you can use it like:

listExtractor(list, edges); //=> [['a', 'b'], ['b', 'c']]

or

var makeEdges = listExtractor(list);
makeEdges([[0, 1], [1, 2], [2, 0]]); //=> [['a', 'b'], ['b', 'c'], ['c', 'a']]