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Reduce array of object to totals by property object

7

0

I'm looking for a smart ES6 way to reduce array of objects into totals-by-property-object.

for a sample data:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

following code:

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

throws an error:

Uncaught TypeError: Cannot read property 'mon' of undefined

even if reduce is initialized with mon:0, tue:0 ... instead of .

Is there a non-for-loop solution?

p.s. expected output is an object where each property is a sum of array objects by that property, e.g. mon:6, tue:3, wed:5, thu:5, fri:8, sat:0, sun:10 in my case

javascript ecmascript-6

share|improve this question

edited 2 days ago

user11154868

asked 2 days ago

user11154868user11154868

384

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7

0

I'm looking for a smart ES6 way to reduce array of objects into totals-by-property-object.

for a sample data:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

following code:

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

throws an error:

Uncaught TypeError: Cannot read property 'mon' of undefined

even if reduce is initialized with mon:0, tue:0 ... instead of .

Is there a non-for-loop solution?

p.s. expected output is an object where each property is a sum of array objects by that property, e.g. mon:6, tue:3, wed:5, thu:5, fri:8, sat:0, sun:10 in my case

javascript ecmascript-6

share|improve this question

edited 2 days ago

user11154868

asked 2 days ago

user11154868user11154868

384

New contributor

user11154868 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

I'm looking for a smart ES6 way to reduce array of objects into totals-by-property-object.

for a sample data:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

following code:

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

throws an error:

Uncaught TypeError: Cannot read property 'mon' of undefined

even if reduce is initialized with mon:0, tue:0 ... instead of .

Is there a non-for-loop solution?

p.s. expected output is an object where each property is a sum of array objects by that property, e.g. mon:6, tue:3, wed:5, thu:5, fri:8, sat:0, sun:10 in my case

javascript ecmascript-6

share|improve this question

edited 2 days ago

user11154868

asked 2 days ago

user11154868user11154868

384

New contributor

user11154868 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

share|improve this question

edited 2 days ago

user11154868

asked 2 days ago

user11154868user11154868

384

New contributor

user11154868 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 2 days ago

user11154868

asked 2 days ago

user11154868user11154868

384

New contributor

user11154868 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 2 days ago

user11154868user11154868

384

New contributor

user11154868 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 2 days ago

user11154868user11154868

384

2 Answers
2

active

oldest

votes

5

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 0) + item[weekday])
 
 return totals;
, );

console.log(res);

share|improve this answer

answered 2 days ago

Ori DroriOri Drori

81.4k138997

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I can't believe it was that close. Thanks a lot.
  
  – user11154868
  2 days ago
  

  
  
  
  

add a comment | 

4

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered 2 days ago

Nina ScholzNina Scholz

195k15107178

add a comment | 

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5

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 0) + item[weekday])
 
 return totals;
, );

console.log(res);

share|improve this answer

answered 2 days ago

Ori DroriOri Drori

81.4k138997

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I can't believe it was that close. Thanks a lot.
  
  – user11154868
  2 days ago
  

  
  
  
  

add a comment | 

5

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 0) + item[weekday])
 
 return totals;
, );

console.log(res);

share|improve this answer

answered 2 days ago

Ori DroriOri Drori

81.4k138997

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I can't believe it was that close. Thanks a lot.
  
  – user11154868
  2 days ago
  

  
  
  
  

add a comment | 

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 0) + item[weekday])
 
 return totals;
, );

console.log(res);

share|improve this answer

answered 2 days ago

Ori DroriOri Drori

81.4k138997

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 0) + item[weekday])
 
 return totals;
, );

console.log(res);

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 0) + item[weekday])
 
 return totals;
, );

console.log(res);

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 0) + item[weekday])
 
 return totals;
, );

console.log(res);

share|improve this answer

answered 2 days ago

Ori DroriOri Drori

81.4k138997

answered 2 days ago

Ori DroriOri Drori

81.4k138997

answered 2 days ago

Ori DroriOri Drori

81.4k138997

4

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered 2 days ago

Nina ScholzNina Scholz

195k15107178

add a comment | 

4

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered 2 days ago

Nina ScholzNina Scholz

195k15107178

add a comment | 

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered 2 days ago

Nina ScholzNina Scholz

195k15107178

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered 2 days ago

Nina ScholzNina Scholz

195k15107178

answered 2 days ago

Nina ScholzNina Scholz

195k15107178

answered 2 days ago

Nina ScholzNina Scholz

195k15107178