如何使用 ramda 过滤嵌套数组中的记录？

Question

I've seen this question in several places but still can't figure this out. Using ramda , how can I filter the following object to return the records that are true for tomatoes ?

[
    {
        "id": "a",
        "name": "fred",
        "food_prefs": {
            "tomatoes": true,
            "spinach": true,
            "pasta": false
        },
        "country": "singapore"
    },
    {
        "id": "b",
        "name": "alexandra",
        "food_prefs": {
            "tomatoes": false,
            "spinach": true,
            "pasta": true
        },
        "country": "france"
    },
    {
        "id": "c",
        "name": "george",
        "food_prefs": {
            "tomatoes": true,
            "spinach": false,
            "pasta": false
        },
        "country": "argentina"
    }
]

Storing this array as myData object, I thought that the following should work:

const R = require("ramda")

const lovesTomatoes = R.pipe ( // taken from: https://stackoverflow.com/a/61480617/6105259
    R.path (["food_prefs"]),
    R.filter (R.prop ("tomatoes"))
)

console.log(lovesTomatoes(myData))

But I end up with the error:

if (typeof obj[methodNames[idx]] === 'function') {

What am I doing wrong?

---

EDIT

---

The answers provided by @Ori Drori and @ThanosDi are both great, but I want to emphasize that a pipe -based solution would be ideal because I have follow-up steps I wish to carry on the filtered array. Consider for example the following array. It's similar the one above, but includes more data: year_born and year_record .

[
    {
        "id": "a",
        "name": "fred",
        "year_born": 1995,
        "year_record": 2010,
        "food_prefs": {
            "tomatoes": true,
            "spinach": true,
            "pasta": false
        },
        "country": "singapore"
    },
    {
        "id": "b",
        "name": "alexandra",
        "year_born": 2002,
        "year_record": 2015,
        "food_prefs": {
            "tomatoes": false,
            "spinach": true,
            "pasta": true
        },
        "country": "france"
    },
    {
        "id": "c",
        "name": "george",
        "year_born": 1980,
        "year_record": 2021,
        "food_prefs": {
            "tomatoes": true,
            "spinach": false,
            "pasta": false
        },
        "country": "argentina"
    }
]

So, for example, to answer a full question such as "for those who love tomatoes, what is the average age at the time of the record creation?"

we would need to:

1. filter the records that love tomates;
2. extract the elements year_born and year_record
3. get the difference between values
4. take the average of the differences

Therefore, using a pipe would be very beneficial.

Answer 1

What went wrong?

You try to get the value of food_prefs out of the array. Since the array doesn't have this key - R.path (["food_prefs"]) is undefined , and then you try to filter this undefined value.

How to solve this problem?

Filter the array, and use R. pathSatisfies R. pathSatisfies for each object to check if a nested property conforms to a criteria. Since the value in this case is a boolean, you can use R.identity as the predicate.

 const { filter, pathSatisfies, identity } = R const lovesTomatoes = filter(pathSatisfies(identity, ['food_prefs', 'tomatoes'])) const data = [{"id":"a","name":"fred","food_prefs":{"tomatoes":true,"spinach":true,"pasta":false},"country":"singapore"},{"id":"b","name":"alexandra","food_prefs":{"tomatoes":false,"spinach":true,"pasta":true},"country":"france"},{"id":"c","name":"george","food_prefs":{"tomatoes":true,"spinach":false,"pasta":false},"country":"argentina"}] const result = lovesTomatoes(data) console.log(result)

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.28.0/ramda.min.js" integrity="sha512-t0vPcE8ynwIFovsylwUuLPIbdhDj6fav2prN9fEu/VYBupsmrmk9x43Hvnt+Mgn2h5YPSJOk7PMo9zIeGedD1A==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

Filtering using a pipe:

Using R.pipe . I wouldn't go this way for a simple filter by nested properties, but you can use a Schwartzian transform . The idea is to create a new array if pairs [value of tomato, original object] , filter by the value of tomato, and then extract the original object:

 const { pipe, map, applySpec, path, identity, filter, last, head } = R const lovesTomatoes = pipe( map(applySpec([path(['food_prefs', 'tomatoes']), identity])), // create an array of [value of tomatoes, original object] filter(head), // filter by the value of the tomatoes map(last) // extract the original object ) const data = [{"id":"a","name":"fred","food_prefs":{"tomatoes":true,"spinach":true,"pasta":false},"country":"singapore"},{"id":"b","name":"alexandra","food_prefs":{"tomatoes":false,"spinach":true,"pasta":true},"country":"france"},{"id":"c","name":"george","food_prefs":{"tomatoes":true,"spinach":false,"pasta":false},"country":"argentina"}] const result = lovesTomatoes(data) console.log(result)

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.28.0/ramda.min.js" integrity="sha512-t0vPcE8ynwIFovsylwUuLPIbdhDj6fav2prN9fEu/VYBupsmrmk9x43Hvnt+Mgn2h5YPSJOk7PMo9zIeGedD1A==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

How to combine the 1st lovesTomatoes filtering function in a pipe:

However, if you just need the pipe to perform other operations on the filtered array, use the filter as one of the steps:

 const { filter, pathSatisfies, identity, pipe, map, prop, uniq } = R const lovesTomatoes = filter(pathSatisfies(identity, ['food_prefs', 'tomatoes'])) const countriesOfTomatoLovers = pipe( lovesTomatoes, map(prop('country')), uniq ) const data = [{"id":"a","name":"fred","food_prefs":{"tomatoes":true,"spinach":true,"pasta":false},"country":"singapore"},{"id":"b","name":"alexandra","food_prefs":{"tomatoes":false,"spinach":true,"pasta":true},"country":"france"},{"id":"c","name":"george","food_prefs":{"tomatoes":true,"spinach":false,"pasta":false},"country":"argentina"}] const result = countriesOfTomatoLovers(data) console.log(result)

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.28.0/ramda.min.js" integrity="sha512-t0vPcE8ynwIFovsylwUuLPIbdhDj6fav2prN9fEu/VYBupsmrmk9x43Hvnt+Mgn2h5YPSJOk7PMo9zIeGedD1A==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

Answer 2

const myData = [
    {
        "id": "a",
        "name": "fred",
        "food_prefs": {
            "tomatoes": true,
            "spinach": true,
            "pasta": false
        },
        "country": "singapore"
    },
    {
        "id": "b",
        "name": "alexandra",
        "food_prefs": {
            "tomatoes": false,
            "spinach": true,
            "pasta": true
        },
        "country": "france"
    },
    {
        "id": "c",
        "name": "george",
        "food_prefs": {
            "tomatoes": true,
            "spinach": false,
            "pasta": false
        },
        "country": "argentina"
    }
];

const lovesTomatoes = filter(pathOr(false, ['food_prefs','tomatoes']));

lovesTomatoes(myData);

Ramda REPL

Answer 3

Ramda comes with a whole suite of predicates built-in already, one of them that I'd use here is pathEq .

I'd suggest to adopt a map and reduce kind of approach, whereas the match function is separated from the actual aggregation...

1. Collect your data point
2. Reduce it to the information you need

 const tomatoLovers = R.filter( R.pathEq(['food_prefs', 'tomatoes'], true), ); const avgAge = R.pipe(R.pluck('age'), R.mean); const data = [{ "id": "a", age: 16, "name": "fred", "food_prefs": { "tomatoes": true, "spinach": true, "pasta": false }, "country": "singapore" }, { "id": "b", age: 66, "name": "alexandra", "food_prefs": { "tomatoes": false, "spinach": true, "pasta": true }, "country": "france" }, { "id": "c", age: 44, "name": "george", "food_prefs": { "tomatoes": true, "spinach": false, "pasta": false }, "country": "argentina" } ] console.log( 'Average age of tomato lovers is:', R.pipe(tomatoLovers, avgAge) (data), ); console.log( 'They are the tomato lovers', R.pipe(tomatoLovers, R.pluck('name')) (data), );

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