How to find the lowest and highest rows in a column vector which contain a value.

So, I have a 20x1 vector (A) shown below. How would I find the row number for the lowest and highest row that contain a value? In the vector below the lowest would be row 6, and the highest would be row 17. Thanks.

A = 
NaN
NaN
NaN
NaN
NaN
1
1
1
NaN
NaN
NaN
1
1
1
NaN
NaN
1
NaN
NaN
NaN

Answer 1

[Akira Agata]

idx = ~isnan(A);
lowestRow = min(find(idx));
highestRow = max(find(idx));

[Nathan B]

Perfect, thank you.

[Jos (10584)]

This is better/faster/easier:

lowestRow = find(idx, 1, 'first')

[Stephen23]

@Jos: that should be an answer.

[Nathan B]

For the code below what would I put where I have written "here" so that the if statement only runs when A is not NaN?

for y = lowestRow:1:highestRow
    if "here"
        disp(A(y))
    end
end

[Jos (10584)]

You also forgot the for-loop counter

for K = lowestRow:highestRow
    if ~isnan(A(K))
       disp(K)
   end
end

However,

tf = ~isnan(A) 
disp( A(tf) )

would almost do the same and is much more efficient

Answer 2

[Jos (10584)]

idx = ~isnan(A);
lowestRow = find(idx, 1, 'first') 
highestRow = find(idx, 1, 'last')

[Nathan B]

Thanks. Also thanks for helping with the if statement.