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Functional Programming Patterns With RamdaJS!

Median Paycheck: Solution Review

Understand how to apply RamdaJS functions to calculate median paychecks from salary data. Learn practical steps including filtering salaries, finding medians, dividing for monthly amounts, and formatting values in a functional programming style.

We'll cover the following...

I hope you didn’t cheat and look at the HOFs section to find this snippet. :D

Either way, let’s list the steps

  1. Get salaries
  2. Reject anything below $100,000
  3. Get the median
  4. Calculate monthly paycheck (amount / 12 months)
  5. Format dollars (USD)

I think we’re comfortable enough to start with a Ramda solution

Javascript (babel-node)
import { filter, map, median, pipe, prop } from 'ramda';
import employees from './employees';
const toUSD = (amount) => amount.toLocaleString('en-US', {
  style: 'currency',
  currency: 'USD',
});
const getMedianPaycheck = pipe(
  map(prop('salary')),
  filter((amount) => amount >= 100000),
  median,
  (amount) => amount / 12,
  toUSD
);
const result = getMedianPaycheck(employees);
console.log({ result });

Remember, pluck('salary') is equivalent to map(prop('salary')).

Javascript (babel-node)
import { filter, median, pipe, pluck } from 'ramda';
import employees from './employees';
const toUSD = (amount) => amount.toLocaleString('en-US', {
  style: 'currency',
  currency: 'USD',
});
const getMedianPaycheck = pipe(
  pluck('salary'),
  filter((amount) => amount >= 100000),
  median,
  (amount) => amount / 12,
  toUSD
);
const result = getMedianPaycheck(employees);
console.log({ result });

And R.lte is great for filtering the salaries.

Javascript (babel-node)
import { filter, lte, median, pipe, pluck } from 'ramda';
import employees from './employees';
const toUSD = (amount) => amount.toLocaleString('en-US', {
  style: 'currency',
  currency: 'USD',
});
const getMedianPaycheck = pipe(
  pluck('salary'),
  filter(lte(100000)),
  median,
  (amount) => amount / 12,
  toUSD
);
const result = getMedianPaycheck(employees);
console.log({ result });

Ramda has a divide function, but it doesn’t work as expected.

Javascript (babel-node)
import { divide, filter, lte, median, pipe, pluck } from 'ramda';
import employees from './employees';
const toUSD = (amount) => amount.toLocaleString('en-US', {
  style: 'currency',
  currency: 'USD',
});
const getMedianPaycheck = pipe(
  pluck('salary'),
  filter(lte(100000)),
  median,
  divide(12),
  toUSD
);
const result = getMedianPaycheck(employees);
console.log({ result });

$0.00?! That doesn’t look right. Let’s inspect with tap.

Javascript (babel-node)
import { divide, filter, lte, median, pipe, pluck, tap } from 'ramda';
import employees from './employees';
const toUSD = (amount) => amount.toLocaleString('en-US', {
  style: 'currency',
  currency: 'USD',
});
const getMedianPaycheck = pipe(
  pluck('salary'),
  filter(lte(100000)),
  median,
  tap((value) => {
    console.log('Before divide:', value);
  }),
  divide(12),
  tap((value) => {
    console.log('After divide:', value);
  }),
  toUSD
);
const result = getMedianPaycheck(employees);
console.log({ result });

Aha! We’re dividing 12 by 608702.5 and getting a tiny decimal that rounds to $0.00! But we want to flip that division! Sounds like a job for Ramda’s flip function.

Javascript (babel-node)
import { divide, filter, flip, lte, median, pipe, pluck, tap } from 'ramda';
import employees from './employees';
const toUSD = (amount) => amount.toLocaleString('en-US', {
  style: 'currency',
  currency: 'USD',
});
const flippedDivide = flip(divide);
const getMedianPaycheck = pipe(
  pluck('salary'),
  filter(lte(100000)),
  median,
  flippedDivide(12),
  toUSD
);
const result = getMedianPaycheck(employees);
console.log({ result });

Looks good to me! flip takes a function and returns a new one with the first two arguments reversed.

https://ramdajs.com/docs/#flip

Again, I wouldn’t do this in the real world. The point’s to expose you to Ramda’s toolkit and let you decide what’s best for your application.