如何用数组中的特殊形式计数相同项目（javascript）

Question

For example:

input: var arr = ['a','b','c','a-5','c-2'];
output: var result = {'a':6,'b':1,'c':'3'} ;

My solution is:

function countSameItem(arr) {
var counter = {};
for (var i = 0; i < arr.length; i++) {
  var item = arr[i].split('-');
  if (item.length === 1) {
    counter[item] = (counter[item] + 1) || 1;
  } else {
    counter[item[0]] = (counter[item[0]] + parseInt(item[1]) || parseInt(item[1]));
  }
}  
return counter;
} 

But I want to thought a more consise solution using the lodash

Answer 1

You can do it concisely without lodash:

var result = ['a','b','c','a-5','c-2'].reduce(function(o, s) {
  var a = s.split('-').concat(1);
  return o[a[0]] = (o[a[0]] || 0) + +a[1], o;
}, Object.create(null));

Answer 2

with lodash you would use the _.reduce function in a similar manner to the way Oriol uses the native reduce function

function countSameItem(arr) {
  return _.reduce( arr, function(counter, n, i) {
    var narr=n.split('-');
    counter[narr[0]] = (counter[narr[0]] || 0) + (1*narr[1] || 1);
    return counter;
  }, {});
}

counter is the accumulator and what is eventually returned from the function.
n is each element
i is the index of each element.

for each element in the input array counter gets the value returned by the last element that was ran. The third argument in _.reduce gives the initial value of counter.

Using the native implementation is probably better unless you are using lodash for other features and want consistency in the code.

The lodash version of reduce does have the benefit of working on objects as well as arrays but this can be done natively as well by using Object.keys(arr).reduce