storing loop function output in vector

Hi, I have a single column array of some positive and negative values. I am trying to use a loop to segregate them and to store the result in a separate vector. Unable to do ot so far. can anyone help please? This is my code:

Diff=MP_25-MP_60

y=nan(117,1)

for i=Diff(1:117) if i>0 y(i) = ('Upward') else y(i) = ('Downward') end end

Answer 1

[David Fletcher]

y=Diff>=0

will return a logical array of all elements in Diff that are greater than or equal to 0. You can either just use this as a marker, or if you wish index out all the positive values (and by extension also all the negative values) into separate vectors: -

positives=Diff(y)
negatives=Diff(~y)

[Ali Ajaz]

Thanks for answering to this question. My problem is I am trying to store the output of the loop as a string into the vector y. But I am unable to do it. Could you please guide me on how to store the output of this for loop in the vector?

[Ali Ajaz]

[David Fletcher]

for a start you won't be able to store 'Upward' and 'Downward' in a matrix without padding them to the same length (and that length will be a minimum of 8 columns ('Downward' has eight letters) not the one you have pre-allocated in y). Would 'U' and 'D' be enough? If you don't want to pad, or contract them down to a single letter, you can allocate to a cell array instead

[Ali Ajaz]

tried, it gives following error: Subscript indices must either be real positive integers or logicals.

[David Fletcher]

Tried what?

[Ali Ajaz]

y=nan(117,1)

for i=Diff(1:117,:) if i>0 y = ('U') else y = ('D') end end

Answer 2

[Ali Ajaz]

y=nan(117,1)

for i=Diff(1:117,:) if i>0 y = ('U') else y = ('D') end end

[David Fletcher]

for iter=1:length(Diff)
    if (Diff(iter)>=0)
        y(iter)='U'
    else
        y(iter)='D'
    end
end

[David Fletcher]

You may find that because you pre-allocated y as NaN, when you add 'U' or 'D' you get their numeric codes instead of the letter.

you could pre-allocate y to a character vector instead

y=repmat('U',117,1)

[David Fletcher]

Actually, if you pre-allocate y to 'D' you can lose the else clause in the condition block (since the array is already set to 'D')

y=repmat('D',117,1)

for iter=1:length(Diff)
    if (Diff(iter)>=0)
        y(iter)='U'
    end
end