How to use if command?

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Iris Li
Iris Li on 21 May 2018
Commented: Iris Li on 21 May 2018
Say I have a table X = (columnA, columnB, columnC) What is wrong with the following command? The result is always columnB = columnA no matter what condition and which line. There are numbers in columnA smaller than 30 or larger than 90 just so you know. Thank you in advance!!
for i = 1:numel(columnA)
if 30 < columnA(i) < 90
columnB(i) = columnA(i);
else
columnB(i) = columnC(i);
end
end
end
  1 Comment
Stephen23
Stephen23 on 21 May 2018
The syntax you use does not do what you think it does. You will need to use
A<X && X<B
The syntax that you used is equivalent to this:
(A<X)<B
You can learn why by reading the MATLAB documentation:

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Accepted Answer

Walter Roberson
Walter Roberson on 21 May 2018
30 < columnA(i) < 90 means the same as ((30 < columnA(i)) < 90) . The first part results in 0 (false) or 1 (true), and that 0 or 1 is then compared to 90 and since both are < 90, the result of the test is always true.
MATLAB does not have any range tests of the form A < x < B , with the exception that such ranges are sometimes recognized in some MATLAB versions but only in calls to piecewise()
  2 Comments
Walter Roberson
Walter Roberson on 21 May 2018
mask = 30 < X.ColumnA & X.ColumnA < 90;
X.ColumnB(mask) = X.ColumnA(mask);
X.ColumnB(~mask) = X.ColumnC(~mask);
Iris Li
Iris Li on 21 May 2018
This is easier than a loop. Thank you!

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