How to tell if there are at least 5 consecutive entries in one 8-by-1 matrix with 8 integers?

Hi:

I am looking for a way to determine if there are AT LEAST 5 consecutive values in one 8-by-1 matrix with 8 integers. The 8 integers do NOT have to be unique. And I prefer this to be short and loop-free.

The consecutive values have to be in a "straight", meaning that [5 1 3 4 2 6 8 7] would work because it has at least 5 (actually 8) consecutive values in a straight. The straight is 1 2 3 4 5 6 7 8.

But [1 2 3 4 10 9 8 7] would not because it only has 4 values in each of the straight. The first straight is 1 2 3 4. The second straight is 7 8 9 10.

Thank you very much for your help (I'm writing this for my TexasHoldEm function for fun)

[Daniel Shub]

First off, this sounds like homework. What have you tried so far? Can you give examples of what should and should not pass your test. Does [5,4,3,2,1,10,20,30] pass? What about [1,3,2,4,5,10,20,30]?

[Daniel Shub]

This sounds to me like a good cody problem, although I really don't know what makes a good cody problem, there are so many ways to do it optimizing it might be fun.

[Azzi Abdelmalek]

Han, it's better if you explain with a numeric example

[Han]

@Azzi: Ok, so [5 1 3 4 2 6 8 7] would work since it has at least 5 (actually 8) consecutive values in a "straight". But something like [1 2 3 4 10 9 8 7] would not work because the longest consecutive value set has only 4 values. Does that answer your question Azzi?

[Azzi Abdelmalek]

Can you explain, in the two cases, what are your consecutive numbers? what means "consecutive in straight"

[Han]

"straight" is a poker term. A straight consists of 5 values. The first value: p (a random integer). Second value: p+1. The third value: p+2. The fourth value: p+3. The fifth value: p+4

[Daniel Shub]

Consider a standard 52 card deck of playing cards where the face cards are represented by 11, 12, and 13. For a 5 card hand, you have a straight if your sorted hand is equal to a:(a+5) for any a. For an 8 card hand you have a 5 card straight if any 5 card subset of your sorted hand is equal to a:(a+5).

[Han]

@Azzi: The straight in [5 1 3 4 2 6 8 7] is 1 2 3 4 5 6 7 8. There are two straights in [1 2 3 4 10 9 8 7], the first one is 1 2 3 4. The second one is 7 8 9 10. Since each straight in the second scenario has a length of 4. It does not qualify the condition I made that each straight has to be at least 5-member long. (but the first one does since it has 8 values)

[Image Analyst]

[5 1 3 4 2 6 8 7] is 1 by 8, not 8 by 1 like you said, and my code assumes. Which is it??? [5; 1; 3; 4; 2; 6; 8; 7] would be 8 by 1.

[Han]

@Image Analyst: You are right, it should be [5 1 3 4 2 6 8 7]'

Answer 1

[Daniel Shub]

As people are giving answers, I am pretty confident that

not(isempty(strfind(diff(sort(unique(x))), ones(1, 4))))

works. I am less confident that

not(all(diff(sort(unique(x)), 4)))

works, but if it does, it is much cooler as I rarely use the second argument to diff. After further thinking the second approach does not work. It fails in all sorts of unique ways, for example 1,3,5,7,9.

[Han]

@Daniel. Thanks, I'll try it in the morning. It's 1am here right now.

[Jan]

You can replace not(isempty(strfind())) by any(strfind())

And the output of unique is still sorted. Then your first method becomes:

any(strfind(diff(unique(x)), ones(1, 4)))

[Han]

any(strfind(diff(unique(x)), ones(1, 4))) it is then. Thanks

Answer 2

[Roger Stafford]

It can all be put into one line:

 any(diff(find([true;diff(unique(x))~=1;true]))>=5)

[Daniel Shub]

Looking at the non sequential entries, nice.

Answer 3

[Image Analyst]

How about

data = [9; 1; 2; 3; 4; 5; 6; 9] % Sample data.
diffData = diff(data)
countOf1s = sum(diffData==1)+1
atLeast5 = countOf1s >= 5

[Daniel Shub]

That says that [1; 2; 3; 5; 6; 7; 9; 10] has at least 5 consecutive entries. Not how I would have defined 5 consecutive, but it might be what the OP is looking for.

[Azzi Abdelmalek]

what about this example?

data = [0; 1; 2; 3; 1; 5; 6; 9] % Sample data.

[Image Analyst]

I assumed integers increasing by one, but I agree that there could be other interpretations of what consecutive means and he should clarify that. Maybe he did when he commented to Azzi "I need at least 5 consecutive values in a "straight". "

I think the best way would be to use bwlabel() in the Image Processing Toolbox followed by regionprops to measure the lengths, but I don't know if he has the Image Processing Toolbox. If you do Han, let me know and there is a simple code that can do it robustly:

data = [9; 1; 2; 3; 4; 5; 6; 9]
%  data = [1; 2; 3; 5; 6; 7; 9; 10]
diffData = diff(data)
labeled = bwlabel(diffData==1)
% Make measurements of all the stretches of numbers increasing by 1
measurements = regionprops(labeled, 'area');
AllLengths = [measurements.Area]
% See if any are more than 5
hasAtLeastOne5 = any(AllLengths > 5)

[Han]

@Azzi: your sample data contains only one straight, it's 0 1 2 3. It has 4 values so it does not satisfy the condition I made that requires at least 5 values.

[Daniel Shub]

@Han Azzi example has two straights/runs 0, 1, 2, 3 and 5, 6.

[Daniel Shub]

@IA I would be surprised if bwlabel followed by regionprops would win Cody or any type of speed test.

[Han]

@Image Analyst Thanks very much for your help. But I do not have image processing toolbox. I heard it's expensive.

Answer 4

[Azzi Abdelmalek]

a=[3 2 3 4 5 5  7 6 8];
e=[1 diff(a)];
e(e==0)=1;
idx=strfind(e,[true,true,true,true]) %  it exist if idx~=0

[Han]

Sorry for the confusion I put in my problem. I need at least 5 consecutive values in a "straight". I guess I forgot to mention that.

[Daniel Shub]

I am confused. When you do e(e==0)=1 you set all the false values equal to true such that all(e) will always return true. You then go looking for a run of trues in a vector of trues.

[Azzi Abdelmalek]

diff(a) can have several values, 0,-1,1,2,....I have grouped 1 and 0

[Daniel Shub]

Of course, apparently I am not thinking straight, but a = ones(1, 8) still passes your test.

Answer 5

[Azzi Abdelmalek]

a=[1; 2; 3; 5; 6; 7; 9; 10]
a=sort(a)
e=[1 ;diff(a)];
e(e==0)=1;
idx=~isempty(strfind(e',[true,true,true,true])) %  it exist if idx=1

[Daniel Shub]

This code doesn't work you need: e=[1 , diff(a)];.

Second, it says a = ones(1, 8) is a straight.

[Azzi Abdelmalek]

Yes, Look at edited answer (e' instead of e), and this is working for a=ones(8,1)