Question 253885 in Javascript Question posted in
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Append value to dictionary of dictionaries in Javascript

I have the following JS code:

var expected_dict = {}
  for (var i = 1; i < expected_data.length; i++) {
    if (expected_data[expected_data[i][0]] == undefined) {
      expected_dict[expected_data[i][0]] = {}
    }
    expected_dict[expected_data[i][0]][expected_data[i][20]] = {}
    expected_dict[expected_data[i][0]][expected_data[i][20]] = expected_data[i][21]
    console.log(expected_dict)
  }

expected_data is an array of arrays, like

[
    ['revisionid1', ..., 'code1', 'cp1']
    ['revisionid1', ..., 'code2', 'cp2']
]

I’d expect the code to add values to the expected_dict revisionid key, but the output ends up being

{ 'revisionid1': { 'code1': 'cp1' } }
{ 'revisionid1': { 'code2': 'cp2' } }

Which means it looks like it’s overwriting the dict each time.
What I want would be

{ 'revisionid1': { 'code1': 'cp1', 'code2': 'cp2'} }

Is there something I’m not understanding about how JS handles dicts?

Tags:

2

Answers


  1. 0

    Try this

    var expected_dict = {};

for (var i = 0; i < expected_data.length; i++) {
  var revisionId = expected_data[i][0];
  var code = expected_data[i][20];
  var cp = expected_data[i][21];

  if (!expected_dict[revisionId]) {
    expected_dict[revisionId] = {}; // Create the inner dictionary if it doesn't exist
  }

  expected_dict[revisionId][code] = cp; // Set the key-value pair in the inner dictionary
}

console.log(expected_dict);
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  2. 0

    Reduce the data to a dict, with the first element as a dict key, the remaining items act as key/value pairs for a dict element:

    const expected_dict = expected_data.reduce((r, item) => 
  item.forEach((v, i) => i && (i + 1)%2 && ((r[item[0]] ??= {})[item[i - 1]] = v)) || r, {});

console.log(expected_dict);
    <script>
const expected_data = [
    ['revisionid1', 'code1', 'cp1'],
    ['revisionid1', 'code2', 'cp2']
];
</script>
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