How to return value by id and not index in ramda?

Question

So I have an array of objects with weekdays, it looks like this:

const weekDays = [
      {
        id: 1,
        name: 'monday'
      },
      {
        id: 2,
        name: 'tuesday'
      },
      {
        id: 3,
        name: 'wednesday'
      },
      {
        id: 4,
        name: 'thursday'
      },
      {
        id: 5,
        name: 'friday'
      },
      {
        id: 6,
        name: 'saturday'
      },
      {
        id: 7,
        name: 'sunday'
      }
    ]

And I have a function for formatting a day, it is used for displaying days in select component, it looks like this:

export const formatDay = flip(nth)(['monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday', 'sunday'])

So this function should return a day name by its id, for example if we pass 1 it should return monday etc., though currently it returns days by their index, so if we pass 1 it returns tuesday, though flip should've dealt with that problem

Answer 1

flip function in your code is not handling the zero-based index of the array properly. The nth function expects a zero-based index, but you are passing the id which starts from 1. You will need to adjust the input to the nth function by subtracting 1 from the input value.

 export const formatDay = (id) => {
      const days = ['monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday', 'sunday'];
      return nth(subtract(id, 1))(days);
    };

const weekDays = [
  {id: 1,name: 'monday'},
  {id: 2,name: 'tuesday'},
  {id: 3,name: 'wednesday'},
  {id: 4,name: 'thursday'},
  {id: 5,name: 'friday'},
  {id: 6,name: 'saturday'},
  {id: 7,name: 'sunday'},
];
const formatDay = (id) => {
  const days = ['monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday', 'sunday'];
  return R.nth(R.subtract(id, 1), days);
};

console.log(formatDay(1)); // Output: "monday"
console.log(formatDay(2)); // Output: "tuesday"
console.log(formatDay(3)); // Output: "wednesday"

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/ramda.min.js"></script>

---

Alternative way:

Leveraging Composition principles:

const formatDay = R.compose(
  R.prop('name'),
  R.flip(R.nth)(weekDays),
  R.dec
);

<script type="module">
import * as R from "https://esm.sh/[email protected]";
const weekDays = [
  {id: 1,name: 'monday'},
  {id: 2,name: 'tuesday'},
  {id: 3,name: 'wednesday'},
  {id: 4,name: 'thursday'},
  {id: 5,name: 'friday'},
  {id: 6,name: 'saturday'},
  {id: 7,name: 'sunday'},
];
const formatDay = R.compose(
  R.prop('name'),
  R.flip(R.nth)(weekDays),
  R.dec
);
console.log(formatDay(1)); // Output: "monday"
console.log(formatDay(2)); // Output: "tuesday"
console.log(formatDay(3)); // Output: "wednesday"
</script>

Answer 2

const { flip, nth } = R

const weekDays = [
  { id: 1, name: 'monday' },
  { id: 2, name: 'tuesday' },
  { id: 3, name: 'wednesday' },
  { id: 4, name: 'thursday' },
  { id: 5, name: 'friday' },
  { id: 6, name: 'saturday' },
  { id: 7, name: 'sunday' }
];

const formatDay = (id) =>
  nth(id - 1, weekDays.map(day => day.name));

console.log(formatDay(1));
console.log(formatDay(2));

<script src="https:////cdn.jsdelivr.net/npm/ramda@latest/dist/ramda.min.js"></script>