MATLAB: Find group number from a range of data that is not fixed

grouprangereturn group numbers

Hello,

I need to solve a problem like below. I have a matrix with 1 column, with unknown number of rows. I have a random number for number of row, and I need to find out that which group is this row in.

Imagine I have this data and I need to found out that row number=10 is in which group ?

My main concern is since I do not know how many groups do I have (inittially unkown) , how should I modify my code?

number_row=randperm(16,1)
if number_row<8
    disp("group 1")
else 
    disp ("group 2")
end

Thanks in advance for help

Best Answer

Are your groups always as you show in your example? That is, group 1 = 1,2,..8 group 2 = 9, 10,..16, group 3 = 17,18, ...24 ?

In this case you can just use

n = 8;  % number of elements in group
maxVal = 290 % put your value here
x = randperm(maxVal,1)
groupNo = floor(x/n) + 1

Related Solutions

MATLAB: Randomly grouping cells in cell array

No need for a loop.

% create 22 names of people (just letters)
names = num2cell(char(97:118));    % {'a' 'b' 'c' ... 'v'} 
number_of_people = numel(names); 
number_of_groups = 6; 
% Create random order of names
randOrder = randperm(numel(names)); 
namesPerm = names(randOrder); 
% Determine number of people per group
groupNum = floor(number_of_people / number_of_groups) + [ones(1,rem(number_of_people,number_of_groups)), zeros(1,number_of_groups - rem(number_of_people,number_of_groups))];
% Create groups
groupIdx = [0,cumsum(groupNum)]; 
nameGroups = arrayfun(@(i){namesPerm(groupIdx(i)+1:groupIdx(i+1))},1:numel(groupNum));

nameGroups is a cell array of 6 groups

nameGroups =
  1×6 cell array
    {1×4 cell}    {1×4 cell}    {1×4 cell}    {1×4 cell}    {1×3 cell}    {1×3 cell}
>>

% Convince yourself that the subgroups do not contain duplicates
% or missing names
numel(unique([nameGroups{:}]))  ==   numel(names)   %should equal 1 | true

To use your loop instead, all you need to do is switch around some of the inputs in mat2cell(). This function drives me crazy sometimes.

grouping = mat2cell(randorder(:), split, 1);
%    Make it a column vector ^^^  ^^^^^^^^ switch those two inputs

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.

Best Answer

Related Solutions

MATLAB: Randomly grouping cells in cell array

MATLAB: Putting similar numbers into groups within an array

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