how to control the string-formatted precision?

[bc0n]

Feature Request: Since Unitful produces strings, I frequently want to control the precision to avoid

a = (1/7)u"mm"
@printf( "%s", a)
> 0.14285714285714285 mm

workaround:

a = (1/7)u"mm"
@printf( "%s", round(typeof(a), a, digits=3))
> 0.143 mm

Rather than trying to mess with the Base.show() functionality, I think an explicit Unitful-to-string function, possibly taking the printf formatting arguments, would be great.

Also, this overload on round() isn't mentioned in the docs, source with kwargs from round

Thanks

[tp2750]

Interestingly DataFrames does some rounding:

julia> DataFrame(a=(1/7)u"mm")
1×1 DataFrame
 Row │ a           
     │ Quantity…   
─────┼─────────────
   1 │ 0.142857 mm

[sostock]

We could either add a new function for this or use IOContext properties. The latter is already in use for formatting exponents in units:

julia> io = IOContext(stdout, :fancy_exponent=>true);

julia> println(u"m/s^2")
m s^-2

julia> println(io, u"m/s^2")
m s⁻²

[sostock]

Interestingly DataFrames does some rounding:

DataFrames probably sets the IOContext property :compact => true, as containers usually do:

julia> println((1/7)u"mm")
0.14285714285714285 mm

julia> println(IOContext(stdout, :compact=>true), (1/7)u"mm")
0.142857 mm