Filtering object by keys in lodash

Question

I wrote the function below to return all keys in an object that match a specific pattern. It seems really round-about because there's no filter function in lodash for objects, when you use it all keys are lost. Is this the only way to filter an objects keys using lodash?

export function keysThatMatch (pattern) {
  return (data) => {
    let x = _.chain(data)
    .mapValues((value, key) => {
      return [{
        key: key,
        value: value
      }]
    })
    .values()
    .filter(data => {
      return data[0].key.match(pattern)
    })
    .zipWith(data => {
      let tmp = {}
      tmp[data[0].key] = data[0].value
      return tmp
    })
    .value()
    return _.extend.apply(null, x)
  }
}

Answer 1

You can use pickBy from lodash to do this. ( https://lodash.com/docs#pickBy )

This example returns an object with keys that start with 'a'

var object = { 'a': 1, 'b': '2', 'c': 3, 'aa': 5};

o2 = _.pickBy(object, function(v, k) {
    return k[0] === 'a';
});

o2 === {"a":1,"aa":5}

Answer 2

I don't think you need lodash for this, I would just use Object.keys , filter for matches then reduce back down to an object like this (untested, but should work):

export function keysThatMatch (pattern) {
  return (data) => {
    return Object.keys(data).filter((key) => {
      return key.match(pattern);
    }).reduce((obj, curKey) => {
      obj[curKey] = data[curKey];
      return obj;
    });
  }
}

Answer 3

Here's a succinct way to do this with lodash - reduce() and set() are your friends.

_.reduce(data, (result, value, key) => key.match(pattern) ? 
  _.set(result, key, value) : result, {});