MATLAB Answers

Trying to extract numbers between bounds and counting them

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Mingjia Wang
Mingjia Wang on 15 Apr 2020
Answered: Tommy on 15 Apr 2020
I'm trying to create a function that finds the amount of numbers in a given table that are greater than or equal to 60 and lower than 70, but I can't us the find function. This is what i have for testing at the moment. The result however always comes out as n = 0 only once. It seems like it either doesnt recognise the x values or it doesn't respect the if statement.
x = randi(100,10,1);
disp(x);
n = 0;
for k = x(:,1)
if (60 <= x) & (x<70)
n = n+1;
disp(n);
end
end
disp(n)
The function itself looks like this
function n = mycount(x)
n = 0;
% Put your code here
for k = x(:,1)
if (60 <= x) & (x<70)
n = n+1;
end
end
end

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Answers (2)

Mohammad Sami
Mohammad Sami on 15 Apr 2020
Edited: Mohammad Sami on 15 Apr 2020
If you can use logical vectors then you can do it like this
x = randi(100,10,1);
count = sum(x >= 60 & x < 70);
If you have to use the for loop, you need to make correction to your loop.
function n = mycount(x)
n = 0;
% Put your code here
for k = 1:length(x)
if x(k) >= 60 & x(k) < 70
n = n+1;
end
end
end

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Tommy
Tommy on 15 Apr 2020
Currently, your for loop only runs once, during which time k is equal to the entirety of x. By using
for k = x(:,1)'
or just
for k = x'
instead, the loop will run 10 times, and on the ith iteration of the loop, k will equal the ith element of x. You should then compare k, not the entirety of x, to 60 and 70:
if (60 <= k) && (k<70)
Better yet, loop through an array of indices of x, rather than x itself:
for i = 1:numel(x)
and then use those indices to determine which element of x to test during a given iteration:
if (60 <= x(i)) && (x(i) < 70)
So in total:
x = randi(100,10,1);
disp(x);
n = 0;
for i = 1:numel(x)
if (60 <= x(i)) && (x(i) < 70)
n = n+1;
disp(n);
end
end
disp(n)

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