# How to create a dynamic array, by counting the content of my current array?

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eirini on 10 Dec 2015
Answered: amal laabidi on 8 May 2021 at 16:51
Hi Matlab friends,
I have an array: A=[1,1,0,0,0,0,1,1,1,0,0,0,1,1]
and I want to create to other (dynamic) arrays, where I will count how many continuous'1' and '0' I have. So, I want to create the new arrays: For '1': B=[2,3,2] For '0': C=[4,3]
Do you know how can I do it?
Regards, Eirini

arich82 on 10 Dec 2015
This is a variation on run length encoding.
Note that find(diff(A)) returns the index of the end of each phase (where a phase is a run of zeros or ones); also note that the last element in A will always be the end of a phase, as well as the element '0' (i.e. the element before A(1)).
Taking the diff of these indices tells you the length of each phase. Putting it all together:
rl = diff([0, find(diff(A)), numel(A)]); % run lengths
B = rl(1:2:end);
C = rl(2:2:end);
Note that whether B corresponds to 1 or 0 depends on A(1); you could either write an if statement to assign B and C accordingly, or do something more obfuscated to assign them automagically.
Please accept this answer if it helps, or let me know in the comments if I've missed something.
arich82 on 10 Dec 2015
For completeness:
2 - A(1) returns 2 if A(1) == 0, and 1 if A(1) == 1|.
Conversely, 1 + A(1) returns 2 if A(1) == 1, and 1 if A(1) == 0.
Therefore, the following code automatically assigns the runlengths of ones to B, and zeros to C:
rl = diff([0, find(diff(A)), numel(A)]); % run lengths
B = rl((2-A(1)):2:end); % rl's of ones
C = rl((1+A(1)):2:end); % rl's of zeros

amal laabidi on 8 May 2021 at 16:51
How to create a dynamic table, to store values measured using a mpu6050 sensor in matlab?
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