Writing CSV files with fixed decimal format

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1

Any option to CSV.write with a format string (e.g. "%.4f")?

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2

I don’t know about CSV.write, but would it work to pre-format the string? I’m thinking something like

using CSV
using Printf
x = 3
CSV.write( @sprintf("%.4f", x)) # Note:I don't recall the CSV.write syntax.

This should be identical to having formatted strings in CSV.write I imagine.

3

I could write a small function to format all floating point numbers in the table, but I was looking for a specific CSV.jl option. The docs don’t mention it, so I am assuming it is not there yet.

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4

I haven’t seen such an option with CSV.jl, and typically do this:

# many table types work – rowtable, columntable, StructArray, DictArray, some others
julia> tbl = (a=1:3, b=rand(3), c=string.(1:3))

julia> using AccessorsExtra
julia> roundedtbl = @modify(x -> @sprintf("%.3f", x), tbl |> RecursiveOfType(Real))
# roundedtbl is the same type of table, but with reals converted to strings

julia> roundedtbl |> CSV.write(...)

Works fine unless you have fancy number types where rounding is more involved. Also, the conversion is not specific to CSV or tables at all, supports basically any struct.

5

CSV.jl has a transform option that can be used with a formatter.
For example:

using CSV, Tables, Printf

M = [rand(5,3) "S" .* string.(1:5)]

transform(col,val) = val
transform(col,val::Float64) = @sprintf("%.2f", val)
CSV.write("formated_floats.csv", Tables.table(M), transform=transform)
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6

Thank you @rafael.guerra , that seems like the best available option. Perhaps the maintainers of CSV.jl can introduce a new numformat similar to dateformat that calls transform as explained above.

7

This is a big pain point for me recently. PrettyTables.jl has good capabilities in this area, but if you are outputting a custom table (rather than using PrettyTables.jl) it is cumbersome to control the precision of output. I’ve resorted to wrapping every number in a formatting function that I supply via keyword argument.

Compounding the problem is that it does not appear to be possible to programmatically vary the format string in @sprintf…

8

Have you looked at Printf.Format()?
For example:

using Printf
w, d = 12, 3
fmt = Printf.Format("%$(w).$(d)f")
Printf.format(fmt, 1e4/rand())