print format adjust decimal point - scala

Question

I like to print a lot of numbers between -1 and 1 and need them to be aligned by the decimal point.
What I get with %2.2f is:
val (a, b) = (0.38, -0.38); println (f"${a}%2.2f\n${b}%2.2f ")
0,38
-0,38
What I like to get is:
0,38
-0,38
Is there an elegant solution?

Answer 1

What you can actually do is to add -+ preceding the formatting likewise:
scala> val (a, b) = (0.38, -0.38); println (f"${a}%-+2.2f\n${b}%-+2.2f")
+0.38
-0.38
a: Double = 0.38
b: Double = -0.38
You will get the + before the number though.
EDIT:
If you know the number of digits of the numbers (the first number of %n.m indicates the length of the digits), you can actually go like:
scala> printf("%5.2f", a);
0.38
scala> printf("%5.2f", b);
-0.38

Answer 2

Although there is already an accepted answer, I'll add one more for future reference. Scala f"" string interpolator actually uses Java formatting infrastructure and in the Java documentation you may find following flag:
' ' '\u0020' Requires the output to include a single extra space ('\u0020') for non-negative values.
So you might actually want to use it. Here is an example that shows the difference:
val arr = Array(0.38, -0.38, 10.38, -10.38, 123.38, -123.38)
println("Without space:")
arr.foreach(a => println(f"${a}%6.2f"))
println("----------------")
println("With space:")
arr.foreach(a => println(f"${a}% 6.2f"))
which produces following output:
Without space:
0,38
-0,38
10,38
-10,38
123,38
-123,38
----------------
With space:
0,38
-0,38
10,38
-10,38
123,38
-123,38
note the difference for 123.38/-123.38 i.e. for the case when there is an "overflow"

Answer 3

The solution is trivial: The first number does not indicate digits before the dot, but digits total, and does not yield to an errormessage, if too short. So for 2 digits after the dot, plus dot, plus one in front and an optional minus sign, I need 5 digits in total, and then it works:
val (a, b) = (0.38, -0.38); println (f"${a}%5.2f\n${b}%5.2f ")
0,38
-0,38
And no, a plus sign is not an option.