# How to print a vector with only 2 decimal places

I’m trying to print a vector x with 2 decimal places, but this:
@sprintf("%.2f ",x)
gives an error:
ERROR: MethodError: no method matching Float64(::Matrix{Float64})

Is there a way to apply “%.2f” to an entire vector or matrix?

Two options include:

julia> using Printf

julia> x = rand(4);

julia> Printf.format.(Ref(Printf.Format("%.2f")), x)
4-element Vector{String}:
"0.81"
"0.67"
"0.31"
"0.11"

julia> string.(round.(x; digits=2))
4-element Vector{String}:
"0.81"
"0.67"
"0.31"
"0.11"

Many thanks!

But I don’t want to print strings, I want the actual value: [0.81,0.67, etc]

just round then

1 Like

Won’t round the actual number? I want to keep the 64-bit number, just print only 2 decimal places.

I’m trying to print a vector x with 2 decimal places

But I don’t want to print strings,

just print only 2 decimal places.

I’m very confused. The number is still 64-bit after rounding.

They want to print, not generate strings.

format.(Ref(stdout), Ref(fmt), x) will print them all.

round.(x; digits=2) will not change the values in x, but create a new array.

Is the question about printing (e.g. to stdout) or the display of the numbers (i.e. in the REPL)?

1 Like
julia> format.(Ref(stdout), Ref(fmt), x)
ERROR: UndefVarError: format not defined

Package?

julia> x = rand(2)
2-element Vector{Float64}:
0.8864506178406879
0.010471246659258249

julia> print(x)
[0.8864506178406879, 0.010471246659258249]

I want to print [0.88, 0.01]

Is that less confusing?

That should do it, thanks! I misunderstood round.

myprint(x) = print(round.(x; sigdigits=2))
1 Like

That’s the solution, thanks!

Same as in the previous suggestion, Printf.

Strange:

julia> using Printf

julia> x=[1.1231233, 2.324234234]
2-element Vector{Float64}:
1.1231233
2.324234234

julia> fmt="%.2f"
"%.2f"

julia> format.(Ref(stdout), Ref(fmt), x)
ERROR: UndefVarError: format not defined
Stacktrace:
[1] top-level scope
@ REPL[5]:1

perhaps a version thing? I am still on Julia 1.6.1.

And:

julia> Printf.format.(Ref(stdout), Ref(fmt), x)
ERROR: MethodError: no method matching format(::Base.TTY, ::String, ::Float64)

But:

julia> Printf.format.(Ref(Printf.Format("%.2f")), x)
2-element Vector{String}:
"1.12"
"2.32"

As easy as:

map(x->@printf("%.2f\n",x), rand(4))
0.64
0.18
0.16
0.94
1 Like

You missed: Printf.format.(Ref(stdout), Ref(Printf.Format("%.2f")), x).

Printf.format requires a Printf.Format object, and it also isn’t exported (unclear why, since it’s the only Printf function I’m aware of that accepts a string variable instead of a string literal). The main Printf interfaces (e.g. @printf and @sprintf) only accept string literals for the formatting string.

Something really has been borged:

julia> using Printf

julia> x=[1.1231233, 2.324234234]
2-element Vector{Float64}:
1.1231233
2.324234234

julia> Printf.format.(Ref(stdout), Ref(Printf.Format("%.2f")), x)
1.122.322-element Vector{Nothing}:
nothing
nothing

But I like that trick:

julia> length(Printf.format.(Ref(stdout), Ref(Printf.Format("%.2f")), x))
1.122.322

But it’s not me, who missed something. I just can’t get it to work. Well, perhaps it isn’t as much important, because I feel, there are better (easier to read) solutions around in this thread.