Add SI-like currency format directive?

[JelleBlaauw]

When I execute the following:

[5,10,15,20].map(v => format('$.1s')(v * 1E9))

it returns:

["$5G", "$10G", "$20G", "$20G"]

However, to me it would make more sense if the combination of SI and currency would not result in G for giga, but B for billion, preferably localized.

Is support for this planned? Thanks.

[mbostock]

This is the intended behavior for s, yes; B is not an SI prefix.

There are currency equivalents in SI for ones (none), thousands (k ↦ K), millions (M), billions (G ↦ B) and trillions (T), but there aren’t equivalents for values outside this range. There’s no common symbol for a quadrillion, for instance, which would use the SI peta prefix P. (Also in finance MM is commonly used instead of M for millions, coming from the Roman for a thousand thousands.)

To support this properly we’d need a different directive than s to format currencies.

[curran]

FWIW replacing "G" with "B" in formatters is something I end up doing frequently.

It would be great to have somthing with that baked in.

[JelleBlaauw]

@mbostock I fully agree with that B for billion is not an SI prefix, and that s shouldn't have to be altered, but instead, a new directive should be added.

About your comment about MM instead of M, I do agree, but I think this also depends on locale, hence my initial note about localization.

[mbostock]

I’ll also mention that number.toLocaleString supports currency formatting, although it does not appear to support abbreviated formats such as millions or billions.

https://observablehq.com/@mbostock/number-formatting

[g3o2]

I wonder whether it would make sense to provide a user property to allow the localising of the SI letters via the d3.formatLocale() function. A user would provide an array of values to applied as a sort of "localised (or rather customised) version of SI", the default being SI itself. For the above request, this would then translate to the following user specification:

numberPrefixes : ["y","z","a","f","p","n","µ","m","","k","M","B","T","P","E","Z","Y"]

[mrlubos]

+1

[mbostock]

Please don’t reply with “+1”. If you want to vote for this issue, click the plus smiley face +😄 at the top of this issue, and then click the 👍 button.

[curran]

What might a solution look like? Perhaps a new thing that is similar to s, but a different letter?

Perhaps

const formatter = number => format('.1s')(number).replace('G', 'B');

could ideally be replaced with

const formatter = format('.1r');

Just picking r out of a hat - could be any letter. Would this approach be reasonable?

Also noting that this issue is not really specific to currency (the "currency" in the title threw me off) - this issue is about replacing G with B generally, I believe.

[mbostock]

r is already used; see the README. But, there are other letters free. 😄

In addition to choosing a letter for the format directive, someone needs to propose a precise definition for this feature. My impression is that this will only support K, M, B and T units? And any value outside that range will behave like the g directive, I suppose?

[curran]

Strawman proposal: exactly the same behavior as s, with the only difference being G switching to B.

[mbostock]

You’d want “K” instead of “k” too, though, no?

Personally, I think it’d be surprising to have SI prefixes mixed in with units that are not SI. Would you rather see “$1,000T” (one thousand trillion dollars) or “$1P” (one petadollars)?

[curran]

Digging into this a bit, found some interesting things:

• english.stackexchange.com: what is the correct abbreviation for millions, billions and trillions in a financial context?

I have seen million, billion, and trillion abbreviated as M, B, and T respectively. However, I would not bet that that is a standard abbreviation.

• Wikipedia: Names of Large Numbers - Interesting tables there of full names, but not abbreviations.

I get what you're saying re: values outside the range of T. The question is how to handle P (Peta-, Quadrillion), E (Exa-, Quintillion), Z (Zetta-, Sextillion), Y (Yotta-, Septillion). Indeed, maybe best leave these out, as you're right that having mixed SI plus this other thing with B (which I don't even know what it is called - "Ordinary Usage"?) would be super confusing.

OK - slightly more nuanced proposal for consideration:

• K instead of k
• M, B and T units
• Beyond T range, express as "$1,000T", "$1,000,000T" etc.