MATLAB: Finding values in an Array

findMATLABstrfind

If I have an array such as

Subject= [126;156;1992, 203, 186]    % First two digits determine group, additional numbers are specific subject within that group.

Is there a method to only read the first two values of each row in order to determine what group the subject is?

Group= [12;15;19;20;18]   %%%This is what I would like the result to be.

Best Answer

Apply some arithmetic:

Subject = [126 156 1992 203 186 10 100 100000]
Group   = fix(Subject ./ (10.^floor(log10(Subject)-1)))

Related Solutions

MATLAB: Putting similar numbers into groups within an array

If you have the Statistics and Machine Learning Toolbox (for pdist2) and the Image Processing Toolbox (for bwlabel), you can do this:

m = [...
7340.1
7340.3
7340.6
7349.0
7349.4
7358.0
7358.1
7358.2
7358.7]
% % New groups would look like follows:
% % Group 1
% 7340.1
% 7340.3
% 7340.6
% % Group 2
% 7349.0
% 7349.4
% % Group 3
% 7358.0
% 7358.1
% 7358.2
% 7358.7]
% First sort m so that close by ones has adjacent indexes.
m = sort(m, 'ascend')
% Get distance of every element to every other element.
distances = pdist2(m, m)
% Find out which pairs are within 2 of each other.
within2 = distances > 0 & distances < 2
% Erase upper triangle to get rid of redundancy
numElements = numel(m);
t = logical(triu(ones(numElements, numElements), 0))
within2(t) = 0
% Label each group with an ID number.
[labeledGroups, numGroups] = bwlabel(within2)
% Put each group into a cell array
for k = 1 : numGroups
  [rows, columns] = find(labeledGroups == k);
  indexes = unique([rows, columns]);
  groups{k} = m(indexes);
end
celldisp(groups); % Display the results in the command window.

It gives you your desired result. Should work for other arrays also, though I didn't test it with any others.

MATLAB: Comparing to string vectors

hey

The way you are defining your arrays causes them to be stored as type int. For example:

date = [12-10-1992;13-10-1992]; -----> date = [-1990,-1989]
date2 = [13-10-1992;14-10-1992]; -----> date2 = [-1989,-1988]

I suppose in this case, you would get lucky because comparing same "dates" would be comparing the integer values, which would turn out to be the same. However, if you actually want to comparing strings, you should define them like this:

date = ['12-10-1992','13-10-1992'];
date2 = ['13-10-1992','14-10-1992'];

Then

find(date == date2)

will return the indices at which the string values are the same

Best Answer

Related Solutions

MATLAB: Putting similar numbers into groups within an array

MATLAB: Comparing to string vectors

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