add leading zeros to number

[Jevon, Graham]

Hi,

 

Does anyone know the expression for adding leading zeros to a number? (i.e. convert 1 to 001 and 12 to 012).

 

I've done this before, but can't remember the expression or find it in the user guide.

 

At  the moment I have a string so my partial expression is value.toNumber()

 

Thanks, Graham

 
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Think before you print

[Parthasarathi Mukhopadhyay]

Dear Graham

In a similar case for us where we need to convert the ID column (1 to 6831) with a prefix (3 alphabets) and 6 places of numbers (like  hlv-000001 to hlv-006831) we have used the following GREL:

"hlv-"+slice("00000"+(rowIndex+1),-6)

Best

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[Adam Gray]

Hi Graham,

Another option may be a variation of this expression, which I've used to pad item identifiers with leading zeros: 

"000"[0,3-value.length()] + value

All credit to University of Texas non-vertebrate Paleontology Lab tutorial (2013!), which I access here: https://wikis.utexas.edu/pages/viewpage.action?pageId=46631837

[Owen Stephens]

Hi Graham,

You can do this with number to string formatting so if you start with the strings "1" and "12" you could use:

value.toNumber().toString("%03d")

It will result in 

1 -> 001

12 -> 012

The documentation for how this works is pretty sparse as it's based on the underlying Java format code which is pretty obscure.

The first part of this document is relatively helpful https://docs.oracle.com/javase/tutorial/java/data/numberformat.html (up to the section on "The DecimalFormat Class" which doesn't apply), and there are lots of examples given in this document https://www.baeldung.com/java-number-formatting

You might be able to find some further helpful examples by googling tutorials on using java format or formatting numbers to strings in java

Best wishes

Owen

[Thad Guidry]

In our docs here GREL functions | OpenRefine we provide a link as shown below to the Formatter class which fully describes all the options available to use.  The tutorial Owen provided covers some of the common uses, but it's quite extensive to do many kinds of formatting conversions.  It's a language in itself!

You can use toString() to convert numbers to strings with rounding, using an optional string format. For example, if you applied the expression value.toString("%.0f") to a column:

Thad

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[Owen Stephens]

On Monday, May 9, 2022 at 2:58:35 PM UTC+1 Thad Guidry wrote:

In our docs here GREL functions | OpenRefine we provide a link as shown below to the Formatter class which fully describes all the options available to use.  

Honestly I find the Java documentation on the formatter class pretty much impossible to use - and I speak as someone who is happy writing code. I almost always have to google for examples or tutorials to find the right incantation for a particular outcome.

[Thad Guidry]

hehehe, yeah understood, I'm just used to it resembling the Fortran alternates back in the days on college DEC's as a wee. :-)

Thad

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[Antoine Beaubien]

I personally like this simple formula that I use in every language:

("000"+ "123").slice(-4)

"123" being the number or sting number I want to pad. If I want a 4 digits number, I add 3x "0" (3x because 4 -1 = 3, I take for granted I never have an empty string, otherwise it's 4), and cut from the right to keep 4 digits.

Very visual and easy to remembre.

Regards, Antoine

[Jevon, Graham]

Thanks Thad, Owen, Parthasarathi

 

("%.0f") is exactly the expression I was looking for. I didn’t think to consider it would be related to .toString.

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