How can we sort a dictionary by value in JavaScript?
A dictionary in Javascript is a data structure that stores values as a key-value pair and is used for easy lookups. The stored values are also called associative arrays, as each entry into the dictionary is a key with an associated value.
Retrieving data
There are two ways to get data from a dictionary:
Object.keys(dictionary): Returns a list of keys from the dictionary.Object.values(dictionary): Returns a list of values from the dictionary.
var dict = {"Alice": 25, "Bob": 22, "James": 15, "Jenifer": 29,"Sarah": 30, "Lukah": 18, "Steve": 41};// Printing the Keys of dict objectconsole.log("Keys in dict Object : ", Object.keys(dict));// Printing the Values of dict objectconsole.log("Values in dict Object: ", Object.values(dict));
Sorting the dictionary by values
There are three steps involved in sorting the dictionary by values:
- We can convert the dictionary into an array of key-value pairs.
- We can sort the list by value.
- We can obtain the keys in the sorted order of the values.
var dict = {"Alice": 25, "Bob": 22, "James": 15, "Jennifer": 29,"Sarah": 30, "Luke": 18, "Steve": 41};// Step - 1// Create the array of key-value pairsvar items = Object.keys(dict).map((key) => { return [key, dict[key]] });// Step - 2// Sort the array based on the second element (i.e. the value)items.sort((first, second) => { return first[1] - second[1] });// Step - 3// Obtain the list of keys in sorted order of the values.var keys = items.map((e) => { return e[0] });console.log(keys);
Step 1
Convert the dictionary into an array of key-value pairs. This process uses the map function to get the items from the dict.
// Step - 1// Create the array of key-value pairsvar items = Object.keys(dict).map((key) => { return [key, dict[key]] });
Step 2
Sort the array with a custom sort function using the second element of the list which is on index 1.
// Step - 2// Sort the array based on the second element (i.e. the value)items.sort((first, second) => { return first[1] - second[1] });
Step 3
Obtain the list of keys in the same order as the sorted values.
// Step - 3// Obtain the list of keys in the same order as the sorted valuesvar keys = items.map((e) => { return e[0] });
Credits
This technique is usually known as the Schwartzian transform. It was first used by Randal Schwartz in 1994, and makes use of the decorate-sort-undecorate idiom.
Schwartz gave the following code to answer a query that asked for a way to sort a list of lines by their last word:
#!/usr/bin/perlrequire 5; # New features, new bugs!map { $_->[0] }sort { $a->[1] cmp $b->[1] }map { [$_, /(\S+)$/] }<>;
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