Customize and abbreviate number_to_human

One of Rails’s most helpful view helpers is number_to_human and it has many options to customise its output. You can read the detailed documentation of its many flexible options.

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e.g.

number_to_human(12_345)        # => "12.3 Thousand"
number_to_human(1_234_567)     # => "1.23 Million"
number_to_human(1_234_567_890) # => "1.23 Billion"

At work, our app displays small cards with large numbers on them and we want to display social media-style counts.

The desired translation from numbers to formatted output is:

1_234         # => "1.2K"
12_345        # => "12.3K"
1_234_567     # => "1.3M"
1_234_567_890 # => "1.2B"

Instead of…

…customising number_to_human whenever you use it:

<%=
number_to_human(
  1_234_567,
  precision: 1,
  significant: false,
  round_mode: :down,
  format: "%n%u",
  units: {thousand: "K", million: "M", billion: "B"}
)
%>

Use…

…customisation in your config/locales/en.yml:

en:
  number:
    human:
      decimal_units:
        format: "%n%u"
        units:
          unit: ""
          thousand: K
          million: M
          billion: B
          trillion: T
          quadrillion: Q

…then use:

number_to_human(1_234_567)
#=> "1.2M"

Or…

…use a specific custom-built helper:

def number_to_human_short(number)
  return number_with_delimiter(number) if number < 10_000
  
  number_to_human(
    number,
    precision: 1,
    significant: false,
    round_mode: :down,
    format: "%n%u",
    units: {
      thousand: "K",
      million: "M",
      billion: "B",
      trillion: "T"
    }
  )
end

…then use:

number_to_human_short(1_234_567)
#=> "1.2M"

Adapted from a great recommendation from Matt Swanson (seen in Chris Oliver’s RailsWorld Talk).

Why?

Rails provides sensible defaults, but you most likely have your own in-house design conventions that probably extend to other elements of your application, like language or number formatting.

In our case we only ever display numbers in the shortened format, so we customised our helpers using the YAML locale files.

If you need more flexibility, or you have multiple number styles, it is better to use a custom helper. In the example above we define a special case with an early return condition that displays all numbers under ten thousand in their entirety, e.g. "9,999" rather than "9.9K".

Why not?

If you’re happy with the defaults, or only need the customisation in one or two locations, this would be an unnecessary level of indirection.

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