Find sequence of numbers in vector

Hi,

we're supposed to find a specific sequence of numbers in a vector using a for and while loop but I don't know how to do it:

"Count the number of times that the sequence 01 occurs in the vector. Find out at which index the sequence 01 has occurred for the 8th times. Try to use the Matlab command for for one of the problems and the Matlab command while for the other problem. For the while-loop make sure that no errors can occur if there is no sequence 01 in the vector a."

This is the vector btw: a = round(rand(1000,1))

This is what I got so far but it doesn't work. Does anybody have any idea on how to do it?

Many thanks,

Debbie

clear;
clc;

a = round(rand(1000,1));
b = (0:1);


for n = 1:length(a)
    strfind (a, b);
end

Error using strfind
Input strings must have one row.

Answer 1

[Jon]

Rather than using strings you can check a condition involving the numerical value of the elements in a, something like

if a(k) == 0 && a(k+1)==1
 ... do something here
end

This will need to be in some kind of a loop to increment the index k and go through all of the elements, be careful to only go up to the second to the last element in the loop otherwise a(k+1) will be past the end of your vector which will cause an error

By the way, although it is not in your assigment, for future reference you can count the number of occurence of 01 in MATLAB using just one line of code:

count = sum(diff(a)==1)

That's the real power of MATLAB

Answer 2

[David Hill]

for-loop

%for loop
a = round(rand(1000,1));
count=0;
eidx=[];
for m=1:length(a)-1
   %look at what this does a(m)==0&&a(m+1)==1
   %use break command once you get to 8 indexes 
end

while loop

%while loop
a = round(rand(1000,1));
count=0;
eidx=[];
m=1;
while count<8&&m<length(a)-1
  %similar here
end

[Dobs]

Thank you! I now have a for loop that tells me how many times the sequence occurs but I don't undestand how to get the while loop to stop after the 8th index.

This is what I got:

a = round(rand(1000,1));
count=0;
eidx=[];
m=1;

while count<8 && m<length(a)-1
  count = count+1;
  if eidx >= 8
      break
  end
end
count

But the resutl is always 8 and that doesn't seem right.

[David Hill]

a = round(rand(1000,1));
count=0;
eidx=[];
m=0;
while count<8 && m<length(a)-1
  m=m+1;
  if a(m)==0&&a(m+1)==1
    count=count+1;
  end
end
if count==8
  eidx=m-1;
end