make_fips_lookup.js

const fs = require('fs')
const path = require('path')

// read the API response files
const DATA_DIR = 'data'
const API_RESPONSE_FILE_PREFIX = 'census_api_response'
const STATES_FILE = path.join(DATA_DIR, `${API_RESPONSE_FILE_PREFIX}_fips_states.json`)
const COUNTIES_FILE = path.join(DATA_DIR, `${API_RESPONSE_FILE_PREFIX}_fips_counties.json`)

const states = JSON.parse(fs.readFileSync(STATES_FILE))
const counties = JSON.parse(fs.readFileSync(COUNTIES_FILE))
const state_abbreviations = JSON.parse(fs.readFileSync('us_state_abbreviations.txt'))
Object.entries(state_abbreviations).forEach(([key, value]) => {
  state_abbreviations[value] = key
})

// First element in the array isn't data but field headers, throw it out
states.shift()
let lookup = states.reduce((accum, [name, fips]) => {
  const abbreviation = state_abbreviations[name]
  if (abbreviation) {
    accum[abbreviation] = {
      '_name': name,
      '_fips': fips
    }
    accum.fipsToState[fips] = abbreviation
  }
  return accum
}, { fipsToState: {} })

// First element in the array isn't data but field headers, throw it out
counties.shift()
counties.reduce((accum, [name, stateFips, fips]) => {
  if (stateFips && fips && lookup.fipsToState[stateFips]) {
    const countyFips = `${stateFips}${fips}`
    const currentState = lookup.fipsToState[stateFips]
    lookup[currentState][name.split(',')[0]] = countyFips
  }
  return lookup
}, lookup)

const FIPS_LOOKUP = path.join(DATA_DIR, 'fips_lookup_by_state.json')
fs.writeFileSync(FIPS_LOOKUP, JSON.stringify(lookup, null, 2))
// console.log(JSON.stringify(lookup, null, 2))
console.log(`wrote lookup file:  ${FIPS_LOOKUP}`)