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Problem 568. Number of 1s in a binary string

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Mayla
Mayla 2023-9-8
评论： Les Beckham 2023-9-8
Thats the question:
Find the number of 1s in the given binary string. Example. If the input string is '1100101', the output is 4. If the input string is '0000', the output is 0
I wrote this code, but I don't understand, what is wrong with it.
function y = one(x)
y = length(find(x))
end

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Les Beckham
Les Beckham 2023-9-8
Ran in:
The find() function returns the index of all non-zero elements in the input. ASCII characters (like '0' and '1') are all non-zero (numerically) so your function will just return the length of the input string.
Example:
find('1011010')
ans = 1×7
1 2 3 4 5 6 7
length(find('1011010'))
ans = 7
There are a lot of ways to solve this problem. Look at this documentation page for one way: find characters
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Mayla
Mayla 2023-9-8
I have already done Onramp. Maybe I should repeat it again :) Do you have any tipps for other free online tutorials?
Les Beckham
Les Beckham 2023-9-8
Mathworks has several other tutorials in addition to the Onramp.
Check this page that lists some more: Self-Paced Online Courses

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Harald
Harald 2023-9-8
Hi,
find is intended for numerical non-0 elements rather than non-'0'. Instead, I would use == to compare to '0', and I would also use sum or nnz rather than length.
Best wishes,
Harald
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Dyuman Joshi
Dyuman Joshi 2023-9-8
Ran in:
"and it didn't work."
Because you are comparing with a numerical value
x='1011010';
x==1
ans = 1×7 logical array
0 0 0 0 0 0 0
What you want to do is compare with a character
x=='1'
ans = 1×7 logical array
1 0 1 1 0 1 0
"And why can't I only use sum(x)?"
Because that will give the sum of the values of x, which is not what the questions asks for.
What you want is, the total number of values i.e. sum where x isequal to '1'. So that's what is done.

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