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search through an array for patterns and put into cell arrays.

Asked by lightroman on 14 Nov 2017
Latest activity Answered by Kelly Kearney
on 14 Nov 2017
Looking to search through a large array of integers and find patterns of up to 1-10 ( can be 1 or 1 2 3 or 1 2 3 4 5 6 .. 10, etc) and place those into cell arrays. Resulting multiple cell arrays of different lengths. A is really long so I was hoping to avoid lengthy loops, in which I figured out a way using ismember and a very very long inefficient loop.
I do not know how many patterns of 1-10 exist. Is this possible? Thanks.
if true
A = [ 1 2 3 78 28 92 1 76 89 23 87 1 2 3 4 5 6 7 8 9 10 72 91 72]
result{1} = {1 2 3}
result{2} = {1}
result{3} = {1 2 3 4 5 6 7 8 9 10}
end

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1 Answer

Answer by Kelly Kearney
on 14 Nov 2017
 Accepted Answer

This sort of problem can usually be solved by using a various combinations of diff:
A = [ 1 2 3 78 28 92 1 76 89 90 23 87 1 2 3 4 5 6 7 8 9 10 72 91 72];
(I modified your example by one element to add a run that didn't start with 1, just in case...)
isnew = [true ~(diff(A) == 1)]; % is each elemet 1 greater than previous?
sidx = find(isnew); % indices of start of each run
nper = diff([sidx length(A)+1]); % number of elements in each run
is1 = A(sidx) == 1; % does run start with 1?
consec = mat2cell(A, 1, nper); % break matrix into cells of runs
consec1 = consec(is1); % keep only cells starting with 1
Result:
>> consec1{:}
ans =
1 2 3
ans =
1
ans =
1 2 3 4 5 6 7 8 9 10

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