Multi tool use

find duplicate obj properties and return lowest count property

Lets say I had an array that looked like:

[
{count: 1, category: 4},
{count: 2, category: 4},
{count: 3, category: 2},
{count: 4, category: 2},
{count: 5, category: 8},
{count: 6, category: 8},
{count: 7, category: 1},
{count: 8, category: 1},
{count: 9, category: 1}
{count: 10, category: 8},
...
]


What I want is to find the lowest count from each category and return a new array of objects. I could easily do this using a plain old loop i think, but would like to use map().reduce or some other new func technique.

4 Answers
4

There are many ways to do it. One would be:

function filterLowestCounts(a) {
const lowestCountsByCategory = a.reduce(
(result, { count, category }) => ({
...result,
[category]: Math.min(count, result[category] || Number.MAX_SAFE_INTEGER)
}),
{}
)

return Object.entries(lowestCountsByCategory).map(
([category, count]) => ({ count, category: Number(category) })
)
}


Call it like this:

filterLowestCounts([
{count: 1, category: 4},
{count: 2, category: 4},
{count: 3, category: 2},
{count: 4, category: 2},
{count: 5, category: 8},
{count: 6, category: 8},
{count: 7, category: 1},
{count: 8, category: 1},
{count: 9, category: 1},
{count: 10, category: 8},
])


Result:

[
{count: 7, category: 1},
{count: 3, category: 2},
{count: 1, category: 4},
{count: 5, category: 8},
]


It looks a little bit messy but this would be an approach to do it in one line using concatenation and nesting of array functions filter, map and reduce:

let array = [
{count: 1, category: 4},
{count: 2, category: 4},
{count: 3, category: 2},
{count: 4, category: 2},
{count: 5, category: 8},
{count: 6, category: 8},
{count: 7, category: 1},
{count: 8, category: 1},
{count: 9, category: 1},
{count: 10, category: 8}
]

let result = array.filter((value, index, self)=>{
return self.findIndex((innerValue)=>{
return innerValue.category == value.category}) === index;
}).map((item)=>{
return { count: array.filter((innerItem)=>{
return innerItem.category == item.category
}).reduce((min, item)=>{
return (item.count < min) ? item.count : min; }).count, category: item.category};
});

console.log(result);

Using Array#reduce() to create object with categories as keys and objects as values then get array using Object#values()

Array#reduce()

Object#values()

const res= Object.values(
data.reduce((acc, {count, category}) => {
const o = acc[category] || (acc[category] = {count, category});
o.count = Math.min(o.count, count);
return acc;
},{})
);

console.log(JSON.stringify(res))

<script>
var data= [
{count: 1, category: 4},
{count: 2, category: 4},
{count: 3, category: 2},
{count: 4, category: 2},
{count: 5, category: 8},
{count: 6, category: 8},
{count: 7, category: 1},
{count: 8, category: 1},
{count: 9, category: 1},
{count: 10, category: 8}

]
</script>

var list = [
{count: 1, category: 4},
{count: 2, category: 4},
{count: 3, category: 2},
{count: 4, category: 2},
{count: 5, category: 8},
{count: 6, category: 8},
{count: 7, category: 1},
{count: 8, category: 1},
{count: 9, category: 1},
{count: 10, category: 8}
];

function groupAndGetMin(list, keyGetter, valueGetter) {
const map = new Map();
list.forEach((item) => {
const key = keyGetter(item);
const value = valueGetter(item);
const o = map.get(key);
if (!o) {
map.set(key, item.count);
} else {
map.set(key, Math.min(o, value));
}
});
return map;
}
var result = groupAndGetMin(list, l => l.category, i => i.count);


// this will return Map(4) {4 => 1, 2 => 3, 8 => 5, 1 => 7}

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