CODEWITHSUNDEEP
matlabvectorcounting
ju.arroyom
ju.arroyom

Reputation: 182

Counting sets and vector positions in Matlab

Suppose I have the following vector in Matlab:

V = [0,1,0,0,0,1,...,1]. The vector only contains 0 and 1s and the total number of entries is 125.

I need to do two things:

First, I need to find the first set of consecutive 1s with exactly eight elements, starting with the last observation.

For example in:

V = [0,1,...,1,1,1,1,1,1,1,1,0,1,0,...,1,1,1,1,1,1,1,1,...,0,0,1,0,1,0,0,1,0,1,...]

I would be interested in identifying the second set on 1s and retrieving the exact position of the last 1 in the set.

My second problem is related to the first one. Once I have the exact position of the last 1 in the set. I need to count six 0s on eight consecutive entries.

In the example given above:

V = [0,1,...,1,1,1,1,1,1,1,1,0,1,0,...,1,1,1,1,1,1,1,1,...,0,0,1,0,1,0,0,1,0,1...]

I would need identify each entry until I found 6 0s in a set of eight.

Upvotes: 1

Views: 61

Answers (1)

zeeMonkeez
zeeMonkeez

Reputation: 5157

This is fun. Not sure this is the best approach, and I don't do any error checking (in case there are no sequences of eight 1s or six 0s):

%// Testing with this vector
v = [0, 0, 1, 0, 1, 1, 1, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0];
n_v = numel(v);
%// The trick is to construct a vector summing eight consecutive entries
v_s = arrayfun(@(ii) sum(v((0:7) + ii)), 1:(n_v - 7));
%// when we find entries equal to 8, we have found eight consecutive 1s
v_8 = find(v_s == 8);
%// Likewise, entries equal to 2 correspond to six zeros (in any order)
v_6_0 = find(v_s == 2);
%// We then find sequence of eight 1s followed by six 0s
v_8_with_6_0 = v_8(arrayfun(@(ii) any(ii<v_6_0), v_8));
%// ... and pick the last one
v_8_with_6_0 = v_8_with_6_0(end);
%// then we get the start of that sequence of 0s
v_6_0_pos = v_6_0(find(v_8_with_6_0 < v_6_0, 1));
%// Print result (add 7 to find last of 8)
fprintf('Last sequence of eight 1s with a following sequence containing six 0s ends at %i, and the sequence of 0s starts at %i.\n', v_8_with_6_0 + 7, v_6_0_pos);

Upvotes: 2

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