CODEWITHSUNDEEP
go
Odinovsky
Odinovsky

Reputation: 555

multidimensional array in golang

Coming from a language that uses array (PHP) and only 3 days of experience in golang, how can I translate a multi-dimensional array assignment using map (or slice, or combination)

I have this code in PHP: $set is a collection of document vectors (string => frequency).

I normally can create a posting statistics like this:

$postinglist = array();  

foreach ($set as $id=>$doc) {
      foreach ($doc as $term => $value) {

      if(!isset($postinglist[$term][$id])) {
          $postinglist[$term][$id] = $value;
      }
}

So it would look something like:

array ( 
   'the' => array ( 
      1 => 5, 
      2 => 10 
      ), 
   'and' => array ( 
      1 => 6, 
      3 => 7
      )
    )

After building my corpus (just array of all terms in all documents), I would then build the posting list for each terms:

$terms = $this->getAllTerms();

foreach($terms as $term) {
    $entry = new EntryStatistics();

    foreach($postinglist[$term] as $id => $value) {
       $post = new PostingStatistics;
       $post->setTf($value);
       $entry->setPostingList($id, $post);
    }
}

I'm wondering if there's a neat way of doing such in golang as I've tried this:

postinglist := make(map[string]map[int]float64)
for id, doc := range indexmanager.GetDocuments() {
  for str, tf := range doc {
      _, ok_pl := postinglist[str][id]
      if !ok_pl {
          postinglist[str] = make(map[int]float64)
          postinglist[str][id] = tf
      }
   }
}

Of course it doesn't work, as it always initializes the map everytime I do:

postinglist[str] = make(map[int]float64)

Upvotes: 6

Views: 5744

Answers (3)

vitr
vitr

Reputation: 7134

If you don't use the zero value in the map, you can take advantage of comparing with nil, as peterSO suggested. In addition, I would encourage you to use custom types, e.g.

type PostStat map[int]float64
type PostList map[string]PostStat

pl := make(PostList)
for id, doc := range indexmanager.GetDocuments() {
    for str, tf := range doc {
        if pl[str] == nil {
            pl[str] = make(PostStat)
        }
        if _, ok := pl[str][id]; !ok {
            pl[str][id] = tf
        }
    }
}

The code above looks a bit clearer and easier to understand, in my opinion.

Upvotes: 0

peterSO
peterSO

Reputation: 166529

Make a map if the map is nil. For example,

package main

import (
    "fmt"
    "math"
)

func main() {
    tests := []struct {
        s string
        i int
        f float64
    }{
        {"s", 42, math.Pi},
        {"s", 100, math.E},
        {"s", 100, 1000.0},
        {"x", 1, 2.0},
    }

    var m map[string]map[int]float64
    fmt.Println(m)
    for _, t := range tests {
        if m == nil {
            m = make(map[string]map[int]float64)
        }
        if m[t.s] == nil {
            m[t.s] = make(map[int]float64)
        }
        m[t.s][t.i] += t.f
        fmt.Println(m)
    }
}

Playground: https://play.golang.org/p/IBZxGgAi6eL

Output:

map[]
map[s:map[42:3.141592653589793]]
map[s:map[42:3.141592653589793 100:2.718281828459045]]
map[s:map[42:3.141592653589793 100:1002.718281828459]]
map[s:map[42:3.141592653589793 100:1002.718281828459] x:map[1:2]]

Upvotes: 4

Odinovsky
Odinovsky

Reputation: 555

I may have to do it like this:

        v_pl, ok_pl := postinglist[str]
        if !ok_pl {
            _, ok_pl2 := v_pl[id]
            if !ok_pl2 {
                postinglist[str] = map[int]float64{id: tf}
            }
        } else {
            _, ok_pl2 := v_pl[id]
            if !ok_pl2 {
                postinglist[str][id] = tf
            }
        }

Upvotes: 0

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