getPhrasesByBlock.js

import { Map, List } from 'immutable';

export default function getPhrasesByBlock(phrases) {
    return phrases.reduce(
        (phrasesByBlock, phrase) => phrasesByBlock.update(
            phrase.get(`blockKey`),
            new List(),
            (blockPhrases) => blockPhrases.push(phrase)
        ),
        new Map(),
    );
}