var censusMembers = Object.freeze([
{
id: 1,
name: 'Bob'
}, {
id: 2,
name: 'Sue'
}, {
id: 3,
name: 'Mary',
household_id: 2
}, {
id: 4,
name: 'Elizabeth',
household_id: 6
}, {
id: 5,
name: 'Tom'
}, {
id: 6,
name: 'Jill'
}, {
id: 7,
name: 'John',
household_id: 6
}
]);This is my array I want to count the number of elements which has household id using ramda function ? how can i do that ?
You can also use R.countBy to count all items that have/don't have household_id using R.has(), and than get the count for true using R.prop():
const { pipe, countBy, has, prop } = R;
const censusMembers = Object.freeze([{"id":1,"name":"Bob"},{"id":2,"name":"Sue"},{"id":3,"name":"Mary","household_id":2},{"id":4,"name":"Elizabeth","household_id":6},{"id":5,"name":"Tom"},{"id":6,"name":"Jill"},{"id":7,"name":"John","household_id":6}]);
const countHouseholders = pipe(
countBy(has('household_id')),
prop('true'),
);
const result = countHouseholders(censusMembers);
console.log(result);<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>has looks to be what you're missing:
var censusMembers = Object.freeze([
{id: 1, name: 'Bob'},
{id: 2, name: 'Sue' },
{id: 3, name: 'Mary', household_id: 2 },
{id: 4, name: 'Elizabeth', household_id: 6},
{id: 5, name: 'Tom'},
{id: 6, name: 'Jill'},
{id: 7, name: 'John', household_id: 6}
]);
const countHouseholders = R.pipe(R.filter(R.has('household_id')), R.length)
console.log(countHouseholders(censusMembers)).as-console-wrapper { max-height: 100% !important; top: 0; }<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>
filter by reject in the above, or wrap has('household_id') in complement. Either should work.Don't use the function filter to count stuff because you're creating an array only to get the length.
You can use the function R.reduce and within the handler, check for the key household_id
var censusMembers = Object.freeze([{id: 1,name: 'Bob'}, {id: 2,name: 'Sue'}, {id: 3,name: 'Mary',household_id: 2}, {id: 4,name: 'Elizabeth',household_id: 6}, {id: 5,name: 'Tom'}, {id: 6,name: 'Jill'}, {id: 7,name: 'John',household_id: 6}]);
// With household_id
// (true is coerced to 1) = 1
console.log("With:", R.reduce((a, c) => ('household_id' in c) + a, 0, censusMembers));
// Without household_id
// !(false is coerced to 0) = 1
console.log("Without:", R.reduce((a, c) => !('household_id' in c) + a, 0, censusMembers));.as-console-wrapper { max-height: 100% !important; top: 0; }<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>censusMembers.reduce(fn, 0) versus R.reduce(fn, 0, censusMembers).) Ramda is all about building and composing functions. I know that this is a learning exercise for the OP, but Ramda is not meant to be a Underscore/lodash replacement; it's meant to make it easier to write FP in JS.
const sum = reduce(add, 0), creating a new function from an old one. It adds little of use to say const myTotal = reduce(add, 0, myNumbers). There's nothing wrong with it, precisely. I would write it that way if I was already using Ramda. But it's not really what Ramda is designed for.
, R.length. But see my answer for a cleaner solution.