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how to extract rows has a same value in column 1 and plot until those rows of column 2 and 3?

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Ram on 23 Apr 2018
Commented: Ram on 29 Jul 2018
Hi everyone, I have a matrix with repeated values in the 1st column, for example:
A = [
1 15 43;
2 05 64;
2 13 32;
3 11 35;
3 01 20;
3 -15 08;
4 46 742;
4 25 234;
..........;]--- let say, there are 2500 rows and repetition values are 2000.
Using A, I am looking to extract data from the 2nd and 3rd column for each value in the 1st column to output B and plot it. Where repetition occurs for a value in the 1st column, the corresponding values in the 2nd and 3rd column are to be plotted (that means 2000 graphs). until end of rows.
I have attempted to use a combination of find functions, if statements and loops, but without success. Ideally, a successful approach would also be efficient, as the actual dataset is large.

Accepted Answer

Ameer Hamza
Ameer Hamza on 23 Apr 2018
You can create a cell array of the separated element as
unique_element = unique(A(:,1));
seperate = cell(numel(unique_element), 1);
for i=1:numel(unique_element)
index = A(:,1)==unique_element(i);
seperate{i} = A(index, 2:3);
The separated values are stored in variable seperate which is a cell array. You can access its values as seperate{1}, seperate{2}, ... or loop through the entire array using for loop and do whatever manipulation or visualization you want on them.
Ram on 29 Jul 2018
@Ameer Hamza, i am unable to extract the index values and tried with loops, find. kindly help where am i doing wrong. comment

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More Answers (1)

Guillaume on 23 Apr 2018
If all you want to do is plot the two columns against each other according to the first column, and assuming that the first column is made of integers from 1 to N without any gap (doesn't have to be ordered though), then this is probably the easiest:
hold on;
splitapply(@plot, A(:, 2), A(:, 3), A(:, 1));
If the first column is not made of integers or has gaps in the integer values, then a findgroup first will work around that:
hold on;
g = findgroups(A(:, 1));
splitapply(@plot, A(:, 2), A(:, 3), g);
Ram on 29 Jul 2018
Hello,i am facing similar problem. my code is
for w =1:length(mydata)
%[~,I]= find(mydata{w, 5}(:,2)) = find(mydata{w, 1}(:,1));
for o = 1:length(mydata{w,5})
index = find(mydata{w, 5}(:,2) == mydata{w, 1}(:,1)== o);
mydata{w,7} = index;
i have a cell which contains max and its index values in each row. Now i want to find max index values in another cell and extract those values( matrix 1*2, here i want to extract only 1st col value only). for ex. [M,I] = [2,295]. 295 index value of its max value in certain row, let say (6,26321) is the extracted index value in another cell. extract value is 6(1st col) similarly all other row cells matrix. Thanks in advance. i tried different ways to get those index values before posting here!

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