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
– alex, Commented Nov 29, 2016 at 14:55

Cerbrus · Accepted Answer · 2016-11-29 15:25:33Z

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, 2016 at 15:25

answered Nov 29, 2016 at 15:01

Cerbrus

73.3k19 gold badges138 silver badges151 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

alex Over a year ago

Strange, the result seems a bit different for me: { 'one two': [ 'one two', 'one two' ] } { 'three four': [ 'three four', 'three four', 'three four' ] }

Cerbrus Over a year ago

@alex: Yes, it generates a single object. This is easier to work with than separate variables.

fafl Over a year ago

When you're already changing the result, just store the count instead: {"one two": 2, "three four": 3}

Hetfield Joe · Accepted Answer · 2016-11-29 15:18:48Z

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 · Accepted Answer · 2016-11-29 16:31:11Z

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, 2016 at 16:31

answered Nov 29, 2016 at 15:21

fafl

7,5074 gold badges32 silver badges54 bronze badges

1 Comment

fafl Over a year ago

[].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.

Collectives™ on Stack Overflow

How to merge identical strings into a single array?

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related