Sort grouped arrays by priority

Question

Sorry for the bad wording, I can't even formulate it in an amicable way, so I'll describe it with examples.

I have a scope of priorities:

const priorities = new Map([
    ['lowest', 1],
    ['low', 2],
    ['high', 3],
    ['highest', 4],
])

I have an array of objects with groups and priorities:

const array = [
    {id: 1, priority: 'high'},
    {id: 2, priority: 'lowest'},
    {id: 3, priority: 'highest'},
    {id: 4, group: 1, priority: 'low'},
    {id: 5, group: 2, priority: 'low'},
    {id: 6, group: 2, priority: 'lowest'},
    {id: 7, group: 2, priority: 'low'},
    {id: 8, group: 1, priority: 'high'}
];

And I have grouped this array to an object with grouped arrays of elements:

const groups = {
    0: [{ id: 1, priority: 'high' }, { id: 2, priority: 'lowest' }, { id: 3, priority: 'highest' }], // have no highest priority for group 0
    1: [{ id: 4, group: 1, priority: 'low' }, { id: 8, group: 1, priority: 'high' }], // high
    2: [{ id: 5, group: 2, priority: 'low' }, { id: 6, group: 2, priority: 'lowest' }, { id: 7, group: 2, priority: 'low' }] // low
};

The priority of the group (except group 0) it's highest priority of the items in this group. I need to pick highest priority from an each group (except group 0) to sort groups and items from group 0 from highest to lowest, it should looks like

[, ..., ... , , <>]

At all, I need sort by group's priority + item without group priority + initial position. E.g. result for the current initial array:

const result = [
    { id: 3, priority: 'highest' },
    { id: 1, priority: 'high' },
    { id: 4, group: 1, priority: 'low' },
    { id: 8, group: 1, priority: 'high' },
    { id: 5, group: 2, priority: 'low' },
    { id: 6, group: 2, priority: 'lowest' },
    { id: 7, group: 2, priority: 'low' },
    { id: 2, priority: 'lowest' },
];

How I could make it?

user_1048572 · Answer

You can

give each item an index, to know their original order. (It might also be possible to rely on sort stability, but it's easier to reason about when being explicit):
```
for (const [i, o] of array.entries()) o.index = i;
```

give each group a key to sort on, which is based on the max priority and first item:

const groupIds = Object.keys(groups).filter(g => g != 0);
groupIds.map(g => {
  let minIndex = Infinity, maxPriority = 0;
  for (const item of groups[g])
    minIndex = Math.min(minIndex, item.index);
    maxPriority = Math.max(maxPriority, priorities.get(item.priority));
  }
  return {group: groups[g], minIndex, maxPriority};
})

add one single-item "group" per ungrouped item:

….concat(groups[0].map(item => {
  return {group: [item], maxPriority: priorities.get(item.priority), minIndex: item.index};
}))

before sorting the array of groups:

….sort((a, b) => b.maxPriority - a.maxPriority || a.minIndex - b.minIndex)

and then joining them together into the result:

….flatMap(({group}) => {
  return group.sort((a, b) => a.index - b.index); // might be unnecessary depending on how you built the group arrays
});

Sort grouped arrays by priority

1 Answers