A reduce method which aggregates common data in objects

Question

I built a method using reduce of JS to aggregate together data from a DB in a better shape.

What I'm wondering is, if that method can be simplified with a more modern approach or better written. Like using a different method instead of a reduce.

The method takes the dbData which includes data in the following form:

const dbData = [{
    studyId: 'X',
    siteId: 'A',
    day: '2000-01-01',
    status: 'PENDING_CALLCENTER',
    current: 5,
    total: 17,
  },
  {
    studyId: 'X',
    siteId: 'A',
    day: '2000-01-01',
    status: 'PENDING_SITE',
    current: 3,
    total: 9,
  },
  {
    studyId: 'Y',
    siteId: 'B',
    day: '2000-01-01',
    status: 'PENDING_SITE',
    current: 3,
    total: 9,
  },
  {
    studyId: 'Y',
    siteId: 'B',
    day: '2000-01-01',
    status: 'PENDING_CALLCENTER',
    current: 3,
    total: 9,
  },
]

The data contains two same fields/values as studyId and siteId and what I aggregate is the status, current, total to be included under the same Study and Site.

The output of the above passing via the method:

[
  {
    "studyId": "X",
    "siteId": "A",
    "currents": {
      "PENDING_CALLCENTER": 5,
      "PENDING_SITE": 3
    },
    "totals": {
      "PENDING_CALLCENTER": 17,
      "PENDING_SITE": 9
    }
  },
  {
    "studyId": "Y",
    "siteId": "B",
    "currents": {
      "PENDING_SITE": 6,
      "PENDING_CALLCENTER": 3
    },
    "totals": {
      "PENDING_SITE": 18,
      "PENDING_CALLCENTER": 9
    }
  }
] 

So it is reduced to a different form where we have one object per studyId and siteId which includes the currents and totals of the status.

The method

dbData.reduce((acc, row) => {
const {
  studyId,
  siteId,
  status,
  current,
  total
} = row;
const idx = acc.findIndex(x => studyId === x.studyId && siteId === x.siteId);
const item = idx === -1 ? {
  studyId,
  siteId,
  currents: {},
  totals: {}
} : { ...acc[idx]
};
item.currents[status] = item.currents[status] ? item.currents[status] + current : current;
item.totals[status] = item.totals[status] ? item.totals[status] + total : total;
if (idx === -1) {
  acc.push(item);
} else {
  acc[idx] = item;
}
return acc;
}, []);

A working example

const dbData = [{
    studyId: 'X',
    siteId: 'A',
    day: '2000-01-01',
    status: 'PENDING_CALLCENTER',
    current: 5,
    total: 17,
  },
  {
    studyId: 'X',
    siteId: 'A',
    day: '2000-01-01',
    status: 'PENDING_SITE',
    current: 3,
    total: 9,
  },
  {
    studyId: 'Y',
    siteId: 'B',
    day: '2000-01-01',
    status: 'PENDING_SITE',
    current: 3,
    total: 9,
  },
  {
    studyId: 'Y',
    siteId: 'B',
    day: '2000-01-01',
    status: 'PENDING_CALLCENTER',
    current: 3,
    total: 9,
  },
];


const reduced = dbData.reduce((acc, row) => {
  const {
    studyId,
    siteId,
    status,
    current,
    total
  } = row;
  const idx = acc.findIndex(x => studyId === x.studyId && siteId === x.siteId);
  const item = idx === -1 ? {
    studyId,
    siteId,
    currents: {},
    totals: {}
  } : { ...acc[idx]
  };
  item.currents[status] = item.currents[status] ? item.currents[status] + current : current;
  item.totals[status] = item.totals[status] ? item.totals[status] + total : total;
  if (idx === -1) {
    acc.push(item);
  } else {
    acc[idx] = item;
  }
  return acc;
}, []);

console.log(reduced);

Answer 1

A couple of things that can be simplified/refactored:

• Conditionals can be reduced to improve code readability.
• No need to clone an object if it already exists. Instead, we can just update the currents and totals properties.

const dbData = [{
    studyId: 'X',
    siteId: 'A',
    day: '2000-01-01',
    status: 'PENDING_CALLCENTER',
    current: 5,
    total: 17,
  },
  {
    studyId: 'X',
    siteId: 'A',
    day: '2000-01-01',
    status: 'PENDING_SITE',
    current: 3,
    total: 9,
  },
  {
    studyId: 'Y',
    siteId: 'B',
    day: '2000-01-01',
    status: 'PENDING_SITE',
    current: 3,
    total: 9,
  },
  {
    studyId: 'Y',
    siteId: 'B',
    day: '2000-01-01',
    status: 'PENDING_CALLCENTER',
    current: 3,
    total: 9,
  },
];


const reduced = dbData.reduce((acc, row) => {
  const {
    studyId,
    siteId,
    status,
    current,
    total
  } = row;
  
  const idx = acc.findIndex(x => studyId === x.studyId && siteId === x.siteId);
  
  if (idx === -1) {
    const item = {
      studyId,
      siteId,
      currents: {
        [status]: current, 
      },
      totals: {
        [status]: total,
      },
    };
    
    acc.push(item);
  } else {
    acc[idx].currents[status] = (acc[idx].currents[status] || 0) + current;
    acc[idx].totals[status] = (acc[idx].totals[status] || 0) + total;
  }
  
  return acc;
}, []);

console.log(reduced);