Indexing with conditions for certain columns

1 次查看（过去 30 天）
Yaser Khojah
Yaser Khojah 2019-3-22
评论： Walter Roberson 2019-3-25
I have a huge matrix where I want to find the indexes that meet each column median only and the rest of the column median should not be included. A manual way to do it is written as below but I need an easier way since my matrix is huge. Thank you so much in advanced.
Matrix_All = rand(1000,3) * 100;
Median_All = median(Matrix_All);
idx_1 = find( Matrix_All(:,1) == Median_All(1) & Matrix_All(:,2) ~= Median_All(2) & Matrix_All(:,3) ~= Median_All(3));
idx_2 = find( Matrix_All(:,1) ~= Median_All(1) & Matrix_All(:,2) == Median_All(2) & Matrix_All(:,3) ~= Median_All(3));
idx_3 = find( Matrix_All(:,1) ~= Median_All(1) & Matrix_All(:,2) ~= Median_All(2) & Matrix_All(:,3) == Median_All(3));
Mat_1 = Matrix_All(idx_1,:);
Mat_2 = Matrix_All(idx_2,:);
Mat_3 = Matrix_All(idx_3,:);
  7 个评论
显示 5更早的评论
Guillaume
Guillaume 2019-3-22
There are no limitation based on the number of columns to doing what you want... whatever that is...
You haven't answered Walter's questions, so we're in the dark about what exactly you're trying to do:
  • what if the median is not found anywhere? e.g. median([1 2 3 4]) is 2.5.
  • what if the median is found multiple time? e,.g median([1 1 2 2 3 3]) is 2
Perhaps, you should explain what the purpose of all this is. Maybe it's not the median that you actually need.
Note that find was completely unnecessary in your code so far.
idx = Matrix_All(:,1) == Median_All(1) & Matrix_All(:,2) ~= Median_All(2) & Matrix_All(:,3) ~= Median_All(3)
Mat_1 = Matrix_All(idx_1,:);
would have produced the same result (or error).
Yaser Khojah
Yaser Khojah 2019-3-25
编辑：Yaser Khojah 2019-3-25
Dear Guiliaume, Sorry I could not get back to you since I did not have access to my MATLAB. Below is what i want to do but not manually since I have to find do that for different criteria.
idx_1 = MaT_All(:,1) == Median_All(1) & MaT_All(:,2) ~= Median_All(2)...
& MaT_All(:,3) ~= Median_All(3) & MaT_All(:,4) ~= Median_All(4)...
& MaT_All(:,5) ~= Median_All(5) & MaT_All(:,6) ~= Median_All(6)...
& MaT_All(:,7) ~= Median_All(7) & MaT_All(:,8) ~= Median_All(8);
Mat_1 = MaT_All(idx_1,:);
scatter(MaT_All(idx_1,18),MaT_All(idx_1,17)); hold on;
idx_2 = MaT_All(:,1) ~= Median_All(1) & MaT_All(:,2) == Median_All(2)...
& MaT_All(:,3) ~= Median_All(3) & MaT_All(:,4) ~= Median_All(4)...
& MaT_All(:,5) ~= Median_All(5) & MaT_All(:,6) ~= Median_All(6)...
& MaT_All(:,7) ~= Median_All(7) & MaT_All(:,8) ~= Median_All(8);
Mat_1 = MaT_All(idx_2,:);
scatter(MaT_All(idx_2,18),MaT_All(idx_2,17)); hold on;
Is it because if the median is found multiple time you only pick one answer where in my case I select all of them?

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2019-3-22
matches_median = bsxfun(@eq, MaT_All, Median_All);
matches_one = find(sum(matches_median,2) == 1);
matches_which = 1 + sum( cumprod(~matches_median(matches_one,:), 2), 2 );
Mat = cell(8,1);
for G = 1 : 8
Mat{G} = MaT_All(matches_one(matches_which==G),:);
end
  2 个评论
Yaser Khojah
Yaser Khojah 2019-3-25
Dear Walter thank you so much for coding this problem. It is not really easy to do it and thank you so much. I'm sorry for coming back late since I could not access MATLAB. Thanks again :).
I’m just wondering when your answer as below, I do not get the same answer my code. Any idea?
figures (yours)
scatter(Mat{1,1}(:,18),Mat{1,1}(:,17))
figures (mine)
idx_1 = MaT_All(:,1) == Median_All(1) & MaT_All(:,2) ~= Median_All(2)...
& MaT_All(:,3) ~= Median_All(3) & MaT_All(:,4) ~= Median_All(4)...
& MaT_All(:,5) ~= Median_All(5) & MaT_All(:,6) ~= Median_All(6)...
& MaT_All(:,7) ~= Median_All(7) & MaT_All(:,8) ~= Median_All(8);
Mat_1 = MaT_All(idx_1,:);
scatter(MaT_All(idx_1,18),MaT_All(idx_1,17)); hold on;
Walter Roberson
Walter Roberson 2019-3-25
The data you have provided us only has 10 columns, so looking at column 18 vs column 17 does not make any sense to us.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Logical 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by