Find average of only directly repeating values in array
조회 수: 3 (최근 30일)
이전 댓글 표시
I have an array with two columns, that I want to clean up by finding the average value of column 1 for each unique value in column 2.
A = [
1 0.1
2 0.2
3 0.2
4 0.4
5 0.2 ]
I tried the unique function but have problems with repeating values (here 0.2 in the last row), so that in the above example I would not just calculate the average of rows 2 and 3, but of 2, 3 and 5. Is there a way to calculate the average of rows 2 and 3 separately from row 5?
댓글 수: 0
채택된 답변
Andrei Bobrov
2017년 12월 7일
ii = [true;diff(A(:,2)) ~= 0];
out = [accumarray(cumsum(ii),A(:,1),[],@mean),A(ii,2)];
추가 답변 (2개)
Akira Agata
2017년 12월 7일
If you have the Image Processing Toolbox, the following code can do that task.
% Sample data
A = [1 0.1;
2 0.2;
3 0.2;
4 0.4;
5 0.2;
6 0.2;
7 0.3];
% Find directly repeating values and assign group ID
idx = diff(A(:,2)) == 0;
idx = [idx; 0] | [0; idx];
group = bwlabel(idx);
% Calculate the average for each group ID
average = splitapply(@mean, A(idx,1), group(idx));
Roger Stafford
2017년 12월 7일
편집: Roger Stafford
2017년 12월 7일
[~,~,n] = unique(A(:,2));
av = accumarray(n,A(:,1),[],@mean);
Note: You should be careful about how the elements in second column of A are generated. Different methods which produce fractions can result in tiny differences due to different round-off errors in what would ordinarily be regarded as like amounts. These would appear in different groups in 'unique'.
As to your question, "Is there a way to calculate the average of rows 2 and 3 separately from row 5?", are you asking a second question here distinct from the first one, or are you somehow trying to figure how to achieve that first objective?
댓글 수: 2
Image Analyst
2017년 12월 7일
Yeah, Niklas, and "each unique value" seems contradictory to "only directly repeating values". So which is it? What about .1 and .4? They are unique values but not repeated values, so how do you want to handle those? Do you want those values in the output or not? Please clarify.
참고 항목
카테고리
Help Center 및 File Exchange에서 Multidimensional Arrays에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!