I'm trying to figure out how to create a lens that'll give me an array of the key values from within an array. Here's a simple example:
const L = require('partial.lenses');
const data = [
{
r: [
{
d: {
one: 1,
two: 2
}
}
]
},
{
r: [
{
d: {
three: 3,
four: 4
}
}
]
}
];
const lens = L.compose (
L.elems,
L.prop ('r'),
L.elems,
L.prop ('d'),
);
const result = L.get (lens, data);
console.log (result);
I want:
[{ one: 1, two: 2 }, { three: 3, four: 4 }]
But get:
{ one: 1, two: 2 }
I'm sure this is trivial, but can't get it quite right. Once my lens correctly selects the array of 'd's I want to use L.modify to get the data with all of the 'd' objects replaced with a string. I think I know how to do once my lens is correct.
Thanks
Use L.collect instead of L.get, L.get returns the first found entity, while L.collect returns all matching entities, similar to [].filter vs [].find.
https://github.com/calmm-js/partial.lenses#l-collect
Related
Having the following array:
const vegsAndFruits = [
{
"fruit_banana": 10,
"fruit_apple": 1,
"veg_tomato": 3,
"fruit_watermelon": 11
},
{
"veg_carrot": 3,
"veg_garlic": 11,
"veg_potato": 0,
"fruit_apricot": 22
},
{
"veg_eggplant": 2,
"veg_cabbage": 1,
"fruit_strawberry": 100,
"fruit_orange": 30
}
]
I want to filter it to return the same array but to keep only the properties that start with "fruit".
Expected output
const expectedOutput = [
{
"fruit_banana": 10,
"fruit_apple": 1,
"fruit_watermelon": 11
},
{
"fruit_apricot": 22
},
{
"fruit_strawberry": 100,
"fruit_orange": 30
}
]
My attempt
I thought the solution should come from mixing ramda's R.startsWith() and R.pickBy(). But the following doesn't work as I expected:
const R = require("ramda")
R.map(R.pickBy(R.startsWith(["fruit"])),vegsAndFruits)
which returns
// [ {}, {}, {} ]
What am I missing here?
The R.pickBy predicate is called with the value (1st) and key (2nd) parameters. Since you need the key, use R.nthArg to create a function that returns the 2nd param:
const { map, pickBy, pipe, nthArg, startsWith } = R
const fn = map(pickBy(pipe(
nthArg(1),
startsWith('fruit')
)))
const vegsAndFruits = [{"fruit_banana":10,"fruit_apple":1,"veg_tomato":3,"fruit_watermelon":11},{"veg_carrot":3,"veg_garlic":11,"veg_potato":0,"fruit_apricot":22},{"veg_eggplant":2,"veg_cabbage":1,"fruit_strawberry":100,"fruit_orange":30}]
const result = fn(vegsAndFruits)
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>
The pickby function takes two parameters, value and key.
You can run R.map(R.pickBy((_, key) => key.startsWith('fruit')),vegsAndFruits) to get the result you want.
I am trying to pass a function that removes duplicates from an array. It should handle strings, object, integers as well. In my code so far I am showing that it will handle strings but nothing else. How can Imake this function universalto handle numbers,handle arrays,handle objects, and mixed types?
let unique = (a) => a.filter((el, i ,self) => self.indexOf(el) ===i);
In this function I hav unique() filtering to make a new array which checks the element and index in the array to check if duplicate. Any help would be appreciated.
i think the first you should do is to sort the array ( input to the function ). Sorting it makes all the array element to be ordered properly. for example if you have in an array [ 1, 3, 4, 'a', 'c', 'a'], sorting this will result to [ 1 , 3 , 4, 'a', 'a' , 'c' ], the next thing is to filter the returned array.
const unique = a => {
if ( ! Array.isArray(a) )
throw new Error(`${a} is not an array`);
let val = a.sort().filter( (value, idx, array) =>
array[++idx] != value
)
return val;
}
let array = [ 1 , 5, 3, 2, "d", "q", "b" , "d" ];
unique(array); // [1, 2, 3, 5, "b", "d", "q"]
let obj = { foo: "bar" };
let arraySize = array.length;
array[arraySize] = obj;
array[arraySize++] = "foo";
array[arraySize++] = "baz";
array[arraySize++] = obj;
unique(array); // [1, 2, 3, 5, {…}, "b", "baz", "d", "foo", "hi", "q"]
it also works for all types, but if you pass in an array literal with arrays or objects as one of its element this code will fail
unique( [ "a", 1 , 3 , "a", 3 , 3, { foo: "baz" }, { foo: "baz" } ] ); // it will not remove the duplicate of { foo: "baz" } , because they both have a different memory address
and you should also note that this code does not return the array in the same order it was passed in , this is as a result of the sort array method
Try using sets without generics. You can write a function as
Set returnUnique(Object array[]) {
Set set=new HashSet();
for (Object obj:array) {
set.add(obj);
}
return set;
}
I have an object with several nested layers of arrays and subobjects, from which I need to extract the values from some paths. Is there some library or native function which can help me do that? I'm already using Lodash and jQuery, but have a hard time figuring out how to simplify this problem.
Example:
{
a: [
{
b: 0,
c: 1
},
{
b: 1,
c: 2
}
]
}
Now I would like to get a list of all a[0..n].b.
My actual object is much larger and has 3 layers of arrays and a path like syn[0].sem[0].pdtb3_relation[0].sense, so I'd rather not write 3 nested for loops if a library function exists.
You can use forEach() to iterate through array.
var o = {
a: [
{
b: 0,
c: 1
},
{
b: 1,
c: 2
}
]
}
Object.keys(o).forEach(a => o[a].forEach(y => console.log(y.b)));
First of all, I'm fairly new to streams, so I'm still getting to grips with some common patterns.
In many libraries we can split a stream into a stream of streams using .groupBy(keySelectorFn). For example, this stream is split into streams based on the value of 'a' in each object (pseudo-code, not based on any particular library):
var groups = Stream.of(
{ a: 1, b: 0 },
{ a: 1, b: 1 },
{ a: 2, b: 2 },
{ a: 1, b: 3 }
)
.groupBy(get('a'));
Say I want to process groups differently based on the value of 'a' of that group:
groups.map(function(group) {
if (..?) {
// Run the group through some process
}
return group;
});
I can't see how to get the value of 'a' without consuming the first element of each group (and if the first element of a group is consumed the group is no longer intact).
This seems to me a fairly common thing that I want to do with streams. Am I taking the wrong approach?
--- EDIT ---
Here's a more specific example of a problem that I'm stuck on:
var groups = Stream.of(
{ a: 1, b: 0 },
{ a: 1, b: 1 },
{ a: 2, b: 0 },
{ a: 2, b: 1 },
{ a: 2, b: 2 },
{ a: 1, b: 2 }
)
.groupBy(get('a'));
How to select the first 1 object where a === 1, and the first 2 objects where a === 2, and pass any other objects straight through? This seems logical to me:
groups.chain(function(group) {
return group.key === 1 ?
group.take(1) :
group.key === 2 ?
group.take(2) :
group ;
});
But group.key does not exist (and even if it did it would seem a bit... smelly).
groupBy will give you a stream of streams(each value in the stream being a stream itself). using fold, you can process each group (which is a stream), into a single value (using conditionals). flatMap puts all the results into a single stream. Here is a simple example that processes groups of objects. It groups the objects according to property "a", does a arithmetic operation based on the value into a single object containing type and val properties. These final objects are flattened into a single stream:
var groupStream = Bacon.fromArray([
{ a: 1, b: 0 },
{ a: 1, b: 1 },
{ a: 2, b: 2 },
{ a: 1, b: 3 }
]);
// -----[stream of objects where a=1]-------[stream of objects where a=2]---->
var groups = groupStream.groupBy(function(k){ return k.a; })
// v is a stream of a=1 objects or a=2 objects
groups.flatMap(function(v) {
//fold(reduce) over the values in v (stream)
return v.fold({type:'', val: 0},function(acc,i) {
if(i.a == 1) {
return {type: 'one', val: acc.val + i.b };
}
if(i.a == 2) {
return {type: 'two', val: acc.val + i.b };
}
})
}).onValue(function(v) {
console.log(v);
});
Here is the jsbin: http://jsbin.com/haliqerita/edit?js,console
Hope that helps.
When running the following query using the root directory of my Firebase, extra nodes are added.
Query:
fire.set({
"users":[
{
"0":[
{
"email":"foobar#gmail.com",
"snake":[
{
"highScore":"15"
}
]
}
]
}
]
});
Result
I get the same result when formatting the data in a json file and importing it directly using the Firebase web interface. Did I miss something in the documentation perhaps?
The issue here is that any time you use array syntax, i.e. [ ... ], you're creating an "array" in Firebase, which we do by just creating an object with numeric keys (i.e. 0, 1, 2, ...).
So if you do:
ref.set({ a: 5 });
The resulting object will be:
{ a: 5 }
But if you instead do:
ref.set([{a: 5}, {b: 6}]);
You'll get:
{
'0': { a: 5 },
'1': { b: 6 }
}
So if you just remove the square brackets from the data you're setting, e.g.:
fire.set({
"users": {
"0": {
"email":"foobar#gmail.com",
"snake": {
"highScore":"15"
}
}
}
});
The resulting data in the web interface should match your data exactly.