Longest Sequence of 1s

I have a code for finding the longest sequence of consecutive ones but I am having problems with certain inputs giving improper results.

    % code
function output=longest_one(n)
b=['0' n '0']
ib=strfind(b,'01')
ie=strfind(b,'10')
il=ie-ib
output=max(il)
if max(n)==0
    output=0
end

When n='1 1 1 1 0 0 0 0 1 1 1 1' is inputted I receive a value of 23 instead of 4.

n =

1 1 1 1 0 0 0 0 1 1 1 1

longest_ones(n) ans = 23

[John BG]

translate from characters with

nn=str2num(n)

you read 23 because your function counts figures and spaces equally, after all they are all characters.

And in 1st line of your function, do you really need to add head and tail zeros?

John

[e-mail]

Answer 1

[Azzi Abdelmalek]

n=[1 1 1 1 0 0 0 1 1 1 1]
longest=max(accumarray(nonzeros((cumsum(~n)+1).*n),1))

If n is a string

n='1 1 1 1 0 0 0 0 1 1 1 1'
n=str2num(n)
longest=max(accumarray(nonzeros((cumsum(~n)+1).*n),1))

Or

out=max(cellfun(@numel,regexp(strrep(n,' ',''),'1+','match')))

[Daniel]

Can you explain "max(accumarray(nonzeros((cumsum(~n)+1).*n),1))" this piece of code? What is the logic to combine all these operatins in such a way?

Thanks :)

Answer 2

[Image Analyst]

This is trivial if you have the Image Processing Toolbox

measurements = regionprops(logical(n), 'Area');
output = max([measurements.Area])

Where n is an array of 0's and 1's - not a string.

Answer 3

[jonas]

Here's another one

%%remove blanks
n= n(find(~isspace(n)));

%%save all trailing ones
out=regexp(n,'1+','match')

%%Find largest
max(cellfun(@numel,out))

edit: did not realize I was late to the party

Answer 4

[Sean de Wolski]

https://www.mathworks.com/help/releases/R2018b/images/ref/bwareafilt.html

biggest = bwareafilt(x, 1)

If x is a char array, then convert it to a double using:

double(split(string(x)))

or

x = x(~isspace(x))-'0'