# sum of array by specific index value

28 views (last 30 days)
Khairul Nur on 29 May 2021
Edited: KALYAN ACHARJYA on 29 May 2021
hi, i have two array. First array containing index and second array (hasil_tambah_array) containing the value to be sum-up as below:
index =
4
2
4
hasil_tambah_array =
3.6881
0.8506
0.0132
0.8506
10.5147
12.5147
14.5074
21.8003
11.2145
18.5074
I try to sum the second array as per index such as 3.6881,0.8506,0.0132 and 0.8506 (since the 1st index is 4) will be sum together . Then 10.5147 and 12.5147 (since the 2nd index is 2) will be sum up and respectively (next will be the rest since the index is 4).
Appreciate ur time to solve this. TQIA.

DGM on 29 May 2021
Edited: DGM on 29 May 2021
This is one way. It's probably not the most efficient way, but it does the job.
idx = [4 2 4];
H = [3.6881 0.8506 0.0132 0.8506 10.5147 12.5147 14.5074 21.8003 11.2145 18.5074].';
S = cellfun(@sum,mat2cell(H,idx,1))
S = 3×1
5.4025 23.0294 66.0296
Bear in mind that using mat2cell() to subdivide the main vector requires that sum(idx) = numel(H), so watch out for that.
Khairul Nur on 29 May 2021
mat2cell working great! TQ!

KALYAN ACHARJYA on 29 May 2021
Edited: KALYAN ACHARJYA on 29 May 2021
result=sum(second_arary(first_array))
More
result=sum(hasil_tambah_array(index))
##### 2 CommentsShowHide 1 older comment
KALYAN ACHARJYA on 29 May 2021
index =[4
2
4];
hasil_tambah_array =[3.6881
0.8506
0.0132
0.8506
10.5147
12.5147
14.5074
21.8003
11.2145
18.5074];
result=sum(hasil_tambah_array(index))
Output:
result =
2.5518
More: Same as
>> 0.8506+0.8506+0.8506
ans =
2.5518