I really need help:(
I have a 2x367 matrix, where the first entry in each row indicates the number of the feature and the second one the number of occurences. I managed to sort them row by row, but I want to sort them pairwise.
So my data looks like:
2490 1
44 512 ......
indicating that I have feature 2490 44 times and 1 512 times. I want to put feature 1 in front but together with the 512..Thanks!
Here is another elegant way (in my opinion):
y = sortrows(x', 1)';
If your expected output is:
1 2490
512 44
you ca use the sort function:
[a,b]=sort(x(1,:))
k=[a;x(2,b)]
The function sort returns as first output the sorted values (in this case the sorte3d values of the first row) and as second output the position index.
You can use the position index to "align" the data of the second row.
Hope this helps.
Qapla'
Related
I need to save the indices of 4 maximum numbers
for example, I need to get the indices of rows 10,9,7,5
5.0259327
4.7127487
4.8435524
4.8538644
5.1048996
6.2441973
5.9413803
6.2912638
5.1117512
5.8309519
5.7419509
6.9663477
5.9958319
6.9519781
6.5802736
6.7327558
7.6765878
I have used
[mA,nA]=max(distA)
where mA is the row and nA is the column
in getting one maximum number but I cannot figure out how to choose another maximum number without duplication. I cannot sort because I need the indices.
You can use the gsort function:
[S,ind]=gsort(distA,"g","d");
The index of the 4 largest elements is the given by
ind(1:4)
You can use this little trick.
[output_val, output_index] = max(input_mat(input_mat < max(input_mat)))
This will give you the value and index of the second largest element. And then similarly, you can do it for 4 numbers.
My goal is to create a random, 20 by 5 array of integers, sort them by increasing order from top to bottom and from left to right, and then calculate the mean in each of the resulting 20 rows. This gives me a 1 by 20 array of the means. I then have to find the column whose mean is closest to 0. Here is my code so far:
RandomArray= randi([-100 100],20,5);
NewArray=reshape(sort(RandomArray(:)),20,5);
MeanArray= mean(transpose(NewArray(:,:)))
X=min(abs(x-0))
How can I store the column number whose mean is closest to 0 into a variable? I'm only about a month into coding so this probably seems like a very simple problem. Thanks
You're almost there. All you need is a find:
RandomArray= randi([-100 100],20,5);
NewArray=reshape(sort(RandomArray(:)),20,5);
% MeanArray= mean(transpose(NewArray(:,:))) %// gives means per row, not column
ColNum = find(abs(mean(NewArray,1))==min(abs(mean(NewArray,1)))); %// gives you the column number of the minimum
MeanColumn = RandomArray(:,ColNum);
find will give you the index of the entry where abs(mean(NewArray)), i.e. the absolute values of the mean per column equals the minimum of that same array, thus the index where the mean of the column is closest to 0.
Note that you don't need your MeanArray, as it transposes (which can be done by NewArray.', and then gives the mean per column, i.e. your old rows. I chucked everything in the find statement.
As suggested in the comment by Matthias W. it's faster to use the second output of min directly instead of a find:
RandomArray= randi([-100 100],20,5);
NewArray=reshape(sort(RandomArray(:)),20,5);
% MeanArray= mean(transpose(NewArray(:,:))) %// gives means per row, not column
[~,ColNum] = min(abs(mean(NewArray,1)));
MeanColumn = RandomArray(:,ColNum);
is there a function in matlab that sums up values starting from the last row and susbstitue the next row with summed values? for example:
data= 1 result 21
2 20
3 18
4 15
5 11
6 6
GameOfThrows is on the right track, but you need an additional flipud when you're done:
out = flipud(cumsum(flipud(data)));
The first flip ensures that we start summing from the last element instead of the first. We then perform our cumulative sum but you also want to be sure that the order is reversed so you have to call flipud one more time. However, to be absolutely safe, because we don't know if your data is a row or column vector, I'm going to ensure that your data is a column vector before doing what you ask:
out = flipud(cumsum(flipud(data(:))));
X =
4 3
8 3
I want to extract the element in each row of X and do some operation on each of them separably (4,3) and (8,3). however the size of may be different based on some parameters in my code, so I want general formula to do such thing,
How I can use the for loop for solving this issue ?
This link shows how to extract specific lines (or columns) from a matrix http://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html
All you have to do is write a loop on an index ii to go through every line.
for ii=1:size(X,1)
a=myfun(X(ii,:));
end
I am currently working on a project in Matlab where I have a cell array of cell arrays. The first cell array is 464 columns long and 1 row deep. Each of these cells is another cell array that is 96 columns and 365 rows. I need to be able to get the mean of the 96 columns for each of the 464 arrays and place each of the 464 arrays on a different row in a new array called mean. I have tried to write code to just do one column as follow:
mean = Homes{1,1}(1:)
But I when ever I try to run this code I got the follow error:
mean = Homes{1,1}(1:)
|
Error: Unbalanced or unexpected parenthesis or bracket.
Basically my final array name mean needs to be 96 columns by 464 rows. I am stuck and could really use your help.
Thank you.
I suggest you to try the following code on a smaller matrix. See if it gives you the desired results.
a=cell(1,4); %for you it will be a=cell(1,464)
for i=1:4
a{i}=randi(10,[5 10]); %for you it will be a{i}=randi(10,[365 96]);
end
a1=cell2mat(a); %just concatenating
a1=mean(a1); %getting the mean for each column. in your case, you should get the mean for 96*464
a2=reshape(a1,[10 4]); %now what reshape does it it takes first 10 elements and arranges it into first column.
%Therefore, since I finally want a 4x10 matrix (in your case 464x96), i.e. mean of 10 elements in first cell array on first row and so on...
%Thus, 1st 10 elements should go to first column after doing reshape (since you want to keep them together). Therefore, instead of directly making matrix as 4x10, first make it as 10x4 and then take transpose (which is the next step).
a2=a2'; %thus you get a 4x10 matrix.
In your case specifically, the code will be
a=cell(1,464);
for i=1:464
a{i}=randi(10,[365 96]);
end
a1=cell2mat(a);
a1=mean(a1);
a2=reshape(a1,[96 365]);
a2=a2';