How can I javascript map array to object by converting an array of objects into a hash map indexed by a specific attribute value? I want to use a string or function to determine the key for the hash map, with the value being the object itself.
function isFunction(func) {
return Object.prototype.toString.call(func) === ‘[object Function]’;
}
/**
- This function converts an array to a hash map
-
@param {String | function} key describes the key to be evaluated in each object to use as key for hashmap
-
@returns Object
- @Example
-
[{id:123, name:'naveen'}, {id:345, name:"kumar"}].toHashMap("id")
-
Returns :- Object {123: Object, 345: Object}
-
-
[{id:123, name:'naveen'}, {id:345, name:"kumar"}].toHashMap(function(obj){return obj.id+1})
-
Returns :- Object {124: Object, 346: Object}
*/
Array.prototype.toHashMap = function(key) {
var _hashMap = {}, getKey = isFunction(key) ? key : function(_obj) { return _obj[key]; };
this.forEach(function (obj) {
_hashMap[getKey(obj)] = obj;
});
return _hashMap;
};
How can I use this function effectively?
Hello! When working with edge cases in JavaScript, it’s essential to handle scenarios where keys may not be unique or could be undefined. Here’s an enhanced version of the toHashMap function that manages duplicate keys by logging a warning and provides flexibility for customization if you want to handle duplicates differently:
Array.prototype.toHashMap = function(key) {
var _hashMap = {};
var getKey = typeof key === 'function' ? key : function(_obj) { return _obj[key]; };
this.forEach(function(obj) {
var keyValue = getKey(obj);
if (keyValue === undefined) {
console.warn("Undefined key encountered. Object skipped:", obj);
return;
}
if (keyValue in _hashMap) {
console.warn(`Duplicate key detected: ${keyValue}`);
// Optionally, handle duplicates here, like appending a counter
}
_hashMap[keyValue] = obj;
});
return _hashMap;
};
// Example usage
var userWithDuplicates = [
{ id: 1, name: 'Alice' },
{ id: 2, name: 'Bob' },
{ id: 1, name: 'David' } // Duplicate ID
];
var userMapWithWarnings = userWithDuplicates.toHashMap("id");
This function will log a warning for any duplicate or undefined keys, allowing you to manage edge cases while ensuring data consistency in your map. Feel free to add logic to handle duplicates as needed, like appending counters or creating an array of objects under the same key.
Using a Function for Dynamic Keys: If you need to compute the key dynamically, you can pass a function that returns the desired key. For instance, if you want to index users by their names:
var userMapByName = users.toHashMap(function(user) {
return user.name.toLowerCase(); // Convert names to lowercase for case-insensitive mapping
});
console.log(userMapByName);
// Output: { alice: { id: 1, name: ‘Alice’ }, bob: { id: 2, name: ‘Bob’ }, charlie: { id: 3, name: ‘Charlie’ } }