How to merge identical strings into a single array?

Question

The following function matches the strings in a file (queries) with the strings of another two files (archives). I included the important logs:

console.log('q:', queries)
console.log('a:', archives)
queries.forEach(query => {
  const regex = new RegExp(query.trim(), 'g')
  archives.forEach(archive => {
    const matched = archive.match(regex)
    console.log('m:', matched)
  })
})

q: [ 'one two', 'three four\n' ]
a: [ 'one two three four three four\n', 'one two three four\n' ]
m: [ 'one two' ]
m: [ 'one two' ]
m: [ 'three four', 'three four' ]
m: [ 'three four' ]

How to modify the code so I merge matched and end up with a result like this?

r1: [ 'one two',  'one two' ]
r2: [ 'three four', 'three four', 'three four' ]

(Maybe I can use .reduce but I'm not very sure how.)

EDIT: I tried this:

  const result = matched.reduce(function (a, b) {
    return a.concat(b)
  }, [])

But ended up with the same result.

the input is what you see in `q:` and `a:`. I want an array for each repeated string. — alex, Nov 29 '16 at 14:55

Cerbrus · Accepted Answer · 2016-11-29T15:25:33.023

1

This should do it:

var queries = [ 'one two', 'three four\n' ],
    archives = [ 'one two three four three four\n', 'one two three four\n' ],
    results = {};

queries.forEach(query => {
  const regex = new RegExp(query.trim(), 'g')
  archives.forEach(archive => {
    const matched = archive.match(regex)
    results[matched[0]] = (results[matched[0]] || []).concat(matched) || matched;
  })
})

console.log(results)

Store the results in an object, using the found string as a key.

For some cleaner data, you can just get the match counts, as fafl suggested:

var queries = [ 'one two', 'three four\n' ],
    archives = [ 'one two three four three four\n', 'one two three four\n' ],
    results = {};

queries.forEach(query => {
  const regex = new RegExp(query.trim(), 'g')
  archives.forEach(archive => {
    const matched = archive.match(regex)
    results[matched[0]] = (results[matched[0]] || 0) + matched.length
  })
})

console.log(results)

edited Nov 29 '16 at 15:25

answered Nov 29 '16 at 15:01

Cerbrus

70,800
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Strange, the result seems a bit different for me: `{ 'one two': [ 'one two', 'one two' ] } { 'three four': [ 'three four', 'three four', 'three four' ] }` – alex Nov 29 '16 at 15:13
@alex: Yes, it generates a single object. This is [easier to work with](http://stackoverflow.com/questions/684672/how-do-i-loop-through-or-enumerate-a-javascript-object) than separate variables. – Cerbrus Nov 29 '16 at 15:21
When you're already changing the result, just store the count instead: `{"one two": 2, "three four": 3}` – fafl Nov 29 '16 at 15:23

score 1 · Answer 2 · answered Nov 29 '16 at 15:18

let queries = [ 'one two', 'three four\n' ],
    archives = [ 'one two three four three four\n', 'one two three four\n' ]

queries.forEach(query => {
  let regex = new RegExp(query.trim(), 'g')

  // first, you need to collect the matched result into a new array
  // forEach will do the process you specified, but won't return any value
  // "map" is the better choice, as it will return the process result
  let result = archives.map(archive => {

    return archive.match(regex)

    // now you could reduce against the new array
  }).reduce(function(a, b) {
    return a.concat(b); 
  }, [])

  console.log(result)

})

One more thing, I don't see "const" will do anything good here, it just let think about why it has to be something unchangeable. So "let" is better to use for reduce the confusion.

fafl · Answer 3 · 2016-11-29T16:31:11.673

1

You don't need reduce for this:

var flatten = arr => [].concat.apply([], arr)
queries.map(q =>
  flatten(
    archives.map(a =>
      a.match((new RegExp(q.trim(), 'g')))
    )
  )
)

edited Nov 29 '16 at 16:31

answered Nov 29 '16 at 15:21

fafl

7,222
3
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`[].concat.apply([], arr)` is used to flatten a 2D array. I don't think there is a better way that involves `spread`. I changed my answer to be a bit more readable. – fafl Nov 29 '16 at 16:29

How to merge identical strings into a single array?

3 Answers3