modificationWithRamda.js

const R = require('ramda')
const initObject = {
    "gold_bid_usd_toz": "1231.66",
    "gold_ask_usd_toz": "1232.66",
    "gold_change_dollar_usd_toz": "9.16",
    "gold_change_percent_usd_toz": "0.74%",
    "gold_high_usd_toz": "1232.21",
    "gold_low_usd_toz": "1221.41",
    "zara_high_credit": "374"
}

const getWordBeforeUnderscore = R.compose(R.head, R.split('_'))

const getUniqKeys = R.compose(R.uniq, R.map(getWordBeforeUnderscore), R.keys)

const modifier = (fn) => (obj) => (acc, val) => {
  return {...acc, [fn(val)]: obj[val]};
}

const filterByStartsWith = R.compose(R.filter, R.startsWith)

const bigObjectReduce = (obj) => (acc, key) => {
  const reduceFn = R.compose(modifier, R.replace(R.__, ''))(`${key}_`)
  const newobjFn = R.compose(R.objOf(key), 
                           R.reduce(reduceFn(obj), {}),
                           filterByStartsWith(key),
                           R.keys)
  return {...acc, ...newobjFn(obj)}
}
R.compose(R.reduce(bigObjectReduce(initObject), {}), getUniqKeys)(initObject)
/*
{
    gold: {
        ask_usd_toz: "1232.66",
        bid_usd_toz: "1231.66",
        change_dollar_usd_toz: "9.16",
        change_percent_usd_toz: "0.74%",
        high_usd_toz: "1232.21",
        low_usd_toz: "1221.41"
    },
    zara: {
        high_credit: "374"
    }
}
*/

refactored.js

const initObject = {
    "gold_bid_usd_toz": "1231.66",
    "gold_ask_usd_toz": "1232.66",
    "gold_change_dollar_usd_toz": "9.16",
    "gold_change_percent_usd_toz": "0.74%",
    "gold_high_usd_toz": "1232.21",
    "gold_low_usd_toz": "1221.41",
    "zara_high_credit": "374"
}

const getWordBeforeUnderscore = R.compose(R.head, R.split('_'))

const getUniqKeys = R.compose(R.uniq, R.map(getWordBeforeUnderscore), R.keys)

const modifier = (fn) => (obj) => (acc, val) => R.merge(acc, {[fn(val)]: obj[val]});


const replaceKeyReducer = R.compose(modifier, R.replace(R.__, ''))

const filterByStartsWith = R.compose(R.filter, R.startsWith)

const buildWithUniqKeys = (obj) => (acc, key) => R.compose(R.merge(acc),
                           R.objOf(key), 
                           R.reduce(replaceKeyReducer(`${key}_`)(obj), {}),
                           filterByStartsWith(key),
                           R.keys)(obj)

R.compose(R.reduce(buildWithUniqKeys(initObject), {}), getUniqKeys)(initObject)