Golang中的多维数组

Question

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)

Answer 1

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]]