Question

93

Using Lodash to sum values by key

rated 0 times [ 95] [ 2] / answers: 1 / hits: 61392 / 8 Years ago, thu, august 4, 2016, 12:00:00

How can I sum the values in objects which share a common key? I need to use Lodash for this because I need good performance if these arrays get huge.

var prjMgrValues = [

   {proj_mgr:Jack ProjManager,submitted_dollars:12000},

   {proj_mgr:Jack ProjManager,submitted_dollars:750000},

   {proj_mgr:Joe ProjManager,submitted_dollars:45000}

]

I'm looking for an output of

[

  {proj_mgr:Jack ProjManager,submitted_dollars:762000},

  {proj_mgr:Joe ProjManager,submitted_dollars:45000}

]

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bobbyw

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2 Years ago

answered 8 Years ago cruzs · Accepted Answer

This is a case of reduction for each unique element.

I always use _.groupBy and then _.map the result to an array after applying the reduction. In this case the reduction operation is _.sumBy.

var prjMgrValues = [

   {proj_mgr:Jack ProjManager,submitted_dollars:12000},

   {proj_mgr:Jack ProjManager,submitted_dollars:750000},

   {proj_mgr:Joe ProjManager,submitted_dollars:45000}

];



var output =

  _(prjMgrValues)

    .groupBy('proj_mgr')

    .map((objs, key) => ({

        'proj_mgr': key,

        'submitted_dollars': _.sumBy(objs, 'submitted_dollars') }))

    .value();



console.log(output);

<script src=https://cdn.jsdelivr.net/lodash/4.14.1/lodash.min.js></script>