Display point labels alternatively to left and right

Question

I am working in QGIS and I have a point layer whose labels are to be displayed left or right of the point. The formula I tried to make it work is, in label placement, selected Offset from Point mode, and built the following expression in the Quadrant:

CASE WHEN ("fid" / 6316) % 2 = 1 THEN 3 ELSE 5 END

Being 6316 the total amount of points in the layer. And 3 and 5, according to the Expression Builder, are:

[0=Above Left|1=Above|2=Above Right|
3=Left|4=Over|5=Right|
6=Below Left|7=Below|8=Below Right]

If I am correct, in this case, if the fid number is odd, it will be placed on the left-hand side, and if the fid number is even, it will be placed on the right-hand side.

At the same time, I wanted them to have 20 mm offset each side, so I built this very similar expression on the Offset X,Y:

CASE WHEN ("fid" / 6316) % 2 = 1 THEN '-20,0' ELSE '20,0' END

However, all the labels display on the same side. I have, of course, made sure that some of the fid numbers are odd and some are even, but it seems I'm missing something pretty obvious here.

Answer 1

It's always good to check the output in the calculator.

% is the modulus operator, which will work directly on the fid, without the need to divide by 6316.

Dividing by 6316 will probably in most cases give you a non-integer eg (1 / 6316) % 2 = 0.000158328. Which does not equal 1, and hence will end up as the ELSE clause!

What you want is just: CASE WHEN "fid" % 2 = 1 THEN 3 ELSE 5 END

One thing to note is that depending on your data, IDs can be negative, in which case odd ones will have a modulus of -1. So consider using abs("fid").