I have an array of objects with the following structure
[{'list': 'one', 'item': 1},
{'list': 'one', 'item': 2},
{'list': 'one', 'item': 3},
{'list': 'two', 'item': 1},
{'list': 'two', 'item': 2}]
Now I need to reformat it as shown below
[{'one': [1, 2, 3]},
{'two': [1, 2]}]
What is the most efficient way to achieve this transformation using the Array.map function?
If you want a solution, consider using Array.prototype.reduce. This method allows you to specify a return value in the callback function for the subsequent call.
var exampleData = [
{ 'group': 'alpha', 'value': 1 },
{ 'group': 'alpha', 'value': 2 },
{ 'group': 'alpha', 'value': 3 },
{ 'group': 'beta', 'value': 1 },
{ 'group': 'beta', 'value': 2 }
],
transformedData = exampleData.reduce(function (result, current) {
result[current.group] = result[current.group] || [];
result[current.group].push(current.value);
return result;
}, {});
document.write('<pre>' + JSON.stringify(transformedData, 0, 4) + '</pre>');Answering your specific query:
// Assuming x is the variable holding your array of objects.
result = {}; // Initialize an empty object to store the output
x.forEach(function (element) { // Utilize this method to loop through each element in the list
result[element.list] = result[element.list] || []; // Taking inspiration from Nina Scholz's solution mentioned below
result[element.list].push(element.item); // Add the outcome to the array
});
If you need to group elements in an array based on multiple properties, a group-by method is what you're after. Take a look at this helpful answer for guidance:
Here's the code snippet:
function groupBy(array, f)
{
var groups = {};
array.forEach(function(o)
{
var group = JSON.stringify(f(o));
groups[group] = groups[group] || [];
groups[group].push(o);
});
return Object.keys(groups).map(function(group)
{
return groups[group];
})
}
var result = groupBy(list, function(item)
{
return [item.lastname, item.age];
});
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