Numeric issue with labels (QGIS adding decimals)

Question

I am encountering numeric issues, possible related to this problem: QGIS labels rounding error

I have a field value of 0.55 (type double NULL) that I want to display in a label as a percentage. The expression for the label is concat(FIELD*100,'%'). The label for this object is shown as 55.00000000000001%.

It only happens for certain values, but always for the same ones: 14% becomes 14.00000000000002 and 28% becomes 28.00000000000004. For other layers, the same thing happens with the ROUND function used in the label expression, for the values 57%, 58% and 110%. The problem recurs whenever those same values come up, in different layers.

Does anyone have this problem, or better yet, found a solution? For now, I get around by adding rounding, or rounding at a different place in the formula.

QGIS version is 3.22.9.

• Babel: So rounding works as you want? So what is the problem? It seems like to be a rounding error (if percent number are calculated based on some values and do not result exactly in what you expect). You vould try converting the numbers to integers, using to_int() function
• MobiMech: Rounding errors occur, but the same numeric issue occurs when I just want to convert a (already rounded) number to a percentage, e.g. 0.55 to 55%. I have work-arounds, but to_int() would probably work too. Thanks for the suggestion.
• Babel: Changing field length might be another option, see: gis.stackexchange.com/a/430360/88814

Answer 1

You can format the number when you change it to a string using the format_number function:

function format_number

Returns a number formatted with the locale separator for thousands. By default the current QGIS user locale is used. Also truncates the decimal places to the number of supplied places.

Syntax

format_number(number[,places=0][,language])

[ ] marks optional components

Arguments

number number to be formatted places integer representing the number of decimal places to truncate the string to. language language (lowercase, two- or three-letter, ISO 639 language code) used to format the number into a string. By default the current QGIS user locale is used.

Examples

format_number(10000000.332,2) → '10,000,000.33' if e.g. the current locale is an English variant format_number(10000000.332,2,'fr') → '10 000 000,33'