Is there a simple way to achieve this with lodash?
_.something([{a: 3, b: 4}, {a: 3, b: 5}, {a: 10}], 'a')
=> { 3: [ {a: 3, b: 4}, {a: 3, b: 5 } ], 10: [{ a: 10 }]}
That is, group all the values that share the same key together as an array under that key.