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[Javascript] Transduce over any Iteratable Collection

JavaScript any collection Over
2023-09-14 08:59:17 时间

So far we've been transducing by manually calling .reduce() on arrays, but we want to be able to transduce over other collection types as well.

In this lesson we'll create a transduce function to support transducing over any data structure that implements the es2015 iterable protocol. We’ll put it to the test by transducing over strings and maps, as well as going from one collection type as input to another as output.

 

The whole point to make transducer work for all iteratable collection is that, iteratable collction can be Map, TypedArray, Array, Set and String.

Current the implement from last post:

[1, 2, 3, 4].reduce(
  compose(isNot2Filter, isEvenFilter, doubleMap)(pushReducer),
  [],
);

const transduce = (xf, reducer, seed, collection) => {
  collection.reduce(xf(reducer), seed)
}

 This implementaion only works for Array type. 

 

If we want Transducer can be used for all Itertable type, we need to change by using 'reduce' to 'for...of' loop.

const transduce = (xf, reducer, seed, collection) => {
  const transformedReducer = xf(reducer);
  let accumulation = seed;
  for (const value of collection) {
    accumulation = transformedReducer(accumulation, value);
  }

  return accumulation;
}

 

Now that, we can use for any iteratable collection not only Array type:

const toUpper = str => str.toUpperCase();
const isVowel = char => ['a', 'e', 'i', 'o', 'u', 'y'].includes(char.toLowerCase());

transduce(
  compose(map(toUpper), filter(isVowel)),
  (str, char) => str + char,
  '',
  'adrian',
); 

const numMap = new Map();
numMap.set('a', 1);
numMap.set('b', 2);
numMap.set('c', 3);
numMap.set('d', 4);

transduce(
  compose(isNot2Filter, isEvenFilter, doubleMap),
  pushReducer,
  [],
  numMap.values(),
);

 

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