Sum of rows with whose row numbers are specified by another array

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Saeid
Saeid 2019-5-31
评论： Saeid 2019-6-10
I have an array of the form:
TTX =
20 9 2 7
40 10 10 1
60 2 10 9
0 10 5 10
40 7 9 7
40 1 2 8
0 3 5 8
60 6 10 4
20 10 8 7
0 10 10 2
I want to add the elements of rows 1:3, then add the elements of the rows 4:5, then 6:end.
How can I do that?
  2 个评论
Stephen23
Stephen23 2019-5-31
@Saeid: you just editted your question, removed the original examples, and asked something different from what you originally asked. This discourages people from helping you.
I already answered your original question, but now my answer makes no sense because you removed all of the relevant information.
In future please use comments for adding new information.

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采纳的回答

Stephen23
Stephen23 2019-5-31
编辑：Stephen23 2019-5-31
From R2015b you can use splitapply:
>> TTX = [...
20 9 2 7
40 10 10 1
60 2 10 9
0 10 5 10
40 7 9 7
40 1 2 8
0 3 5 8
60 6 10 4
20 10 8 7
0 10 10 2];
>> [U,~,X] = unique(TTX(:,1));
>> Y = splitapply(@(x)sum(x,1),TTX(:,2:4),X);
>> M = [U,Y]
M =
0 23 20 20
20 19 10 14
40 18 21 16
60 8 20 13
EDIT: this matches the original question's output explanation and example.
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Stephen23
Stephen23 2019-5-31
编辑：Stephen23 2019-5-31
@Saeid: read about repelem, use it to generate an index vector. Apply that indexing vector to the column indices of your array:
>> R = [3,5,2];
>> X = repelem(1:numel(R),R);
>> M = randi(9,5,3)
M =
2 6 7
4 1 7
9 8 4
8 9 6
9 7 2
>> M(:,X)
ans =
2 2 2 6 6 6 6 6 7 7
4 4 4 1 1 1 1 1 7 7
9 9 9 8 8 8 8 8 4 4
8 8 8 9 9 9 9 9 6 6
9 9 9 7 7 7 7 7 2 2

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