javascript - At underscore js, Can I get multiple columns with pluck method after input where method as linq select projection

Question

var people = [
    {firstName : "Thein", city : "ny", qty : 5},
    {firstName : "Michael", city : "ny", qty : 3},
    {firstName : "Bloom", city : "nj", qty : 10}
];

var results=_.pluck(_.where(people, {city : "ny"}), 'firstName');

For example : I need firstName and qty.

question from:https://stackoverflow.com/questions/19349881/at-underscore-js-can-i-get-multiple-columns-with-pluck-method-after-input-where

Answer 1

To project to multiple properties, you need map, not pluck:

var results = _.map(
    _.where(people, {city : "ny"}), 
    function(person) {
        return { firstName: person.firstName, qty: person.qty };
    }
);

[{"firstName":"Thein","qty":5},{"firstName":"Michael","qty":3}]

(Fiddle)

Note that, if you wanted to, you could create a helper method "pluckMany" that does the same thing as pluck with variable arguments:

// first argument is the source array, followed by one or more property names
var pluckMany = function() {
    // get the property names to pluck
    var source = arguments[0];
    var propertiesToPluck = _.rest(arguments, 1);
    return _.map(source, function(item) {
        var obj = {};
        _.each(propertiesToPluck, function(property) {
            obj[property] = item[property]; 
        });
        return obj;
    });
};

You can use the _.mixin function to add a "pluckMany" function to the _ namespace. Using this you can write simply:

var results = _.chain(people).where({city : "ny"}).pluckMany( "firstName", "qty").value();

(Fiddle)