For X of Y loop counters

Naim Published at Dev

Naim

I have this standings array

    { pos: 1, competitor_id: 583, rating: 2049, tier: 1 },
    { pos: 2, competitor_id: 862, rating: 1818, tier: 1 },
    { pos: 3, competitor_id: 67, rating: 1762, tier: 1 },
    { pos: 4, competitor_id: 758, rating: 1750, tier: 1 },
    { pos: 5, competitor_id: 713, rating: 1735, tier: 1 },
    { pos: 6, competitor_id: 868, rating: 1730, tier: 1 },
    { pos: 7, competitor_id: 946, rating: 1706, tier: 2 },
    { pos: 8, competitor_id: 893, rating: 1705, tier: 2 },
    { pos: 9, competitor_id: 731, rating: 1695, tier: 2 },
    { pos: 10, competitor_id: 869, rating: 1692, tier: 2 },
    { pos: 11, competitor_id: 998, rating: 1672, tier: 2 },
    { pos: 12, competitor_id: 968, rating: 1661, tier: 2 },
    { pos: 13, competitor_id: 460, rating: 1656, tier: 2 },
    { pos: 14, competitor_id: 879, rating: 1648, tier: 2 },
    { pos: 15, competitor_id: 969, rating: 1631, tier: 2 },
    { pos: 16, competitor_id: 925, rating: 1629, tier: 2 },
    { pos: 17, competitor_id: 999, rating: 1626, tier: 2 },
    { pos: 18, competitor_id: 991, rating: 1619, tier: 2 },
    { pos: 19, competitor_id: 956, rating: 1618, tier: 2 },
    { pos: 20, competitor_id: 711, rating: 1617, tier: 2 },
    { pos: 21, competitor_id: 964, rating: 1616, tier: 2 },

I want to increment tier by one every time we move 6 rows down. As you can see above it switches to tier 2 properly but fails to increment to 3 at pos:13 and to tier 4 at pos:19

I tried

const tiersize = 6;
// setting the counters
let tiercounter = 1;
let limit = tiersize;
// running the loop
for (const row of standings) {
  await connectionPromise
    .query({
      sql: 'update table set tier = ? where competitor_id = ?'
    }, [tiercounter, row.competitor_id], );
  if (row.pos == limit) {
    tiercounter += 1;
    limit += tiersize;
  }
}

What am I doing wrong?

Barmar

You're updating the database, but you're not updating the array as well. Add row.tier = tiercounter; to the loop.

const tiersize = 6;
// setting the counters
let tiercounter = 1;
let limit = tiersize;
// running the loop
for (const row of standings) {
  await connectionPromise
    .query({
      sql: 'update table set tier = ? where competitor_id = ?'
    }, [tiercounter, row.competitor_id], );
  row.tier = tiercounter;
  if (row.pos == limit) {
    tiercounter += 1;
    limit += tiersize;
  }
}

But rather than incrementing tiercounter as you go, you can simply calculate it from pos.

tiercounter = Math.floor((row.pos-1) / tiersize) + 1;

The updated code would then be:

const tiersize = 6;
// running the loop
for (const row of standings) {
  let tiercounter = Math.floor((row.pos - 1) / tiersize) + 1;
  await connectionPromise
    .query({
      sql: 'update table set tier = ? where competitor_id = ?'
    }, [tiercounter, row.competitor_id], );
  row.tier = tiercounter;
}

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