When I need to draw datapoints from a external data file I’m using lua, like this:

\starttext

\startluacode

Elemento = {}

x = {}

y ={}

z= {}

carga = {}

i=1

context("\\startMPcode”)

context("numeric u; u := 1.5cm;")

for line in io.lines("molecule.xyz") do

local a, b, c, d, e = string.match(line, '(%a+)%s*%s*(%S+)%s*%s*(%S+)%s*%s*(%S+)%s*%s*(%S+)')

Elemento[i]= a

x[i]= tonumber(b)

y[i]= tonumber(c)

z[i]= tonumber(d)

carga[i]= tonumber(e)

context("label(\"%s\", (%0.6f u, %0.6f u));", a, x[i],y[i])

i=i+1

end

context("\\stopMPcode”)

\stopluacode

\stoptext

Is there a way to pass directly the external data to MetaPost without using Lua?

I know that I can use a similar function to gdata from graph.mp. I try to reuse this piece of code, but not works.

\startMPcode

vardef Grdln_@#(expr f) =

save n_, s_; string s_;

s_ = readfrom f;

string @#[];

if s_<>EOF:

@#1 := loptok s_;

n_ = if @#1="%": 0 else: 1 fi;

forever:

@#[incr n_] := loptok s_;

exitif @#[n_]=" ";

endfor

@#1<>" "

else: false

enddef;

\stopMPcode