Write float arrays to a text file
You are encouraged to solve this task according to the task description, using any language you may know.
Write two equal-sized numerical arrays `x' and `y' to a two-column text file named `filename'.
The first column of the file contains values from an `x'-array with a given `xprecision', the second -- values from `y'-array with `yprecision'.
For example, considering:
x = {1, 2, 3, 1e11};
y = {1, 1.4142135623730951, 1.7320508075688772, 316227.76601683791}; /* sqrt(x) */
xprecision = 3;
yprecision = 5;
The file is:
1 1 2 1.4142 3 1.7321 1e+011 3.1623e+005
This task is intended as a subtask for Measure relative performance of sorting algorithms implementations.
Ada
<Ada> with Ada.Text_IO; use Ada.Text_IO; with Ada.Float_Text_IO; use Ada.Float_Text_IO; with Ada.Numerics.Elementary_Functions; use Ada.Numerics.Elementary_Functions;
procedure Write_Float_Array is
type Float_Array is array (1..4) of Float;
procedure Write_Columns
( File : File_Type;
X : Float_Array;
Y : Float_Array;
X_Pres : Natural := 3;
Y_Pres : Natural := 5
) is
begin
for I in Float_Array'range loop
Put (File => File, Item => X(I), Fore => 1, Aft => X_Pres - 1);
Put (File, " ");
Put (File => File, Item => Y(I), Fore => 1, Aft => Y_Pres - 1);
New_Line (File);
end loop;
end Write_Columns;
File : File_Type;
X : Float_Array := (1.0, 2.0, 3.0, 1.0e11);
Y : Float_Array;
begin
Put ("Tell us the file name to write:");
Create (File, Out_File, Get_Line);
for I in Float_Array'range loop
Y(I) := Sqrt (X (I));
end loop;
Write_columns (File, X, Y);
Close (File);
end Write_Float_Array; </Ada>
Fortran
In ANSI FORTRAN 77 or later use OPEN STATEMENT, and formatted WRITE statement with implied DO loop:
real x(4), y(4)
data x / 1.0, 2.0, 4.0, 1.0e11 /
do 10 i = 1, 4
y = sqrt(x)
10 continue
open(unit=15, file='two_cols.txt', status='new')
write(15,'(f20.3,f21.4)') (x(I), y(I), I = 1, 4)
end
IDL
; the data:
x = [1,2,3,1e11]
y=sqrt(x)
xprecision=3
yprecision=5
; NOT how one would do things in IDL, but in the spirit of the task - the output format:
form = string(xprecision,yprecision,format='("(G0.",I0.0,",1x,G0.",I0.0,")")')
; file I/O:
openw,unit,"datafile.txt",/get
for i = 1L, n_elements(x) do printf, unit, x[i-1],y[i-1],format=form
free_lun,unit
The file "datafile.txt" then contains the following:
1 1 2 1.4142 3 1.7321 1E+011 3.1623E+005
This is fairly ugly and un-IDLish. For example one shouldn't just rely on x and y having the same size. And if data is output in human-readable form, it should probably be lined up more nicely. And if it really has to be in two-column format with x and y side by side, one might consider running ASCII_Template or some such instead of that ugly hand-formatting.
J
require 'files' NB. for fwrites x =. 1 2 3 1e11 y =. %: x NB. y is sqrt(x) xprecision =. 3 yprecision =. 5 filename =. 'whatever.txt' data =. (0 j. xprecision,yprecision) ": x,.y data fwrites filename
Python
import itertools
def writedat(filename, x, y, xprecision=3, yprecision=5):
with open(filename,'w') as f:
for a, b in itertools.izip(x, y):
f.write("%.*g\t%.*g\n" % (xprecision, a, yprecision, b))
Example usage
>>> import math
>>> x = [1, 2, 3, 1e11]
>>> y = map(math.sqrt, x)
>>> y
[1.0, 1.4142135623730951, 1.7320508075688772, 316227.76601683791]
>>> writedat("sqrt.dat", x, y)
>>> # check
...
>>> for line in open('sqrt.dat'):
... print line,
...
1 1
2 1.4142
3 1.7321
1e+011 3.1623e+005