storing loop function output in vector

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Ali Ajaz
Ali Ajaz 2018-3-18
评论： David Fletcher 2018-3-18
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

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David Fletcher
David Fletcher 2018-3-18
编辑：David Fletcher 2018-3-18
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)
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Ali Ajaz
Ali Ajaz 2018-3-18
y=nan(117,1)
for i=Diff(1:117,:) if i>0 y = ('U') else y = ('D') end end

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Ali Ajaz
Ali Ajaz 2018-3-18
y=nan(117,1)
for i=Diff(1:117,:) if i>0 y = ('U') else y = ('D') end end
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David Fletcher
David Fletcher 2018-3-18
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
David Fletcher 2018-3-18
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

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