How to use if command？

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

[Stephen23]

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:

https://www.mathworks.com/help/matlab/matlab_prog/operator-precedence.html

https://www.mathworks.com/help/matlab/ref/lt.html

Answer 1

[Walter Roberson]

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()

[Walter Roberson]

mask = 30 < X.ColumnA & X.ColumnA < 90;
X.ColumnB(mask) = X.ColumnA(mask);
X.ColumnB(~mask) = X.ColumnC(~mask);

[Iris Li]

This is easier than a loop. Thank you!