NumPy Input and Output: savetxt() function

Last update on August 19 2022 21:50:38 (UTC/GMT +8 hours)

numpy.savetxt() function

The savetxt() function is used to save an array to a text file.

Syntax:

numpy.savetxt(fname, X, fmt='%.18e', delimiter=' ', newline='\n', header='', footer='', comments='#', encoding=None)

Version: 1.15.0

Parameter:

Name	Description	Required / Optional
fname	If the filename ends in .gz, the file is automatically saved in compressed gzip format. loadtxt understands gzipped files transparently. filename or file handle	Required
X	Data to be saved to a text file. 1D or 2D array_like	Required
fmt	A single format (%10.5f), a sequence of formats, or a multi-format string, e.g. 'Iteration %d – %10.5f', in which case delimiter is ignored. For complex X, the legal options for fmt are: a. a single specifier, fmt='%.4e', resulting in numbers formatted like '(%s+%sj)’ % (fmt, fmt) b. a full string specifying every real and imaginary part, e.g. '%.4e %+.4ej %.4e %+.4ej %.4e %+.4ej' for 3 columns c. a list of specifiers, one per column - in this case, the real and imaginary part must have separate specifiers, e.g. ['%.3e + %.3ej', '(%.15e%+.15ej)'] for 2 columns str or sequence of strs	Optional
delimiter	String or character separating columns. str	Optional
newline	String or character separating lines. str	Optional
header	String that will be written at the beginning of the file. str	Optional
footer	String that will be written at the end of the file. str	Optional
comments	String that will be prepended to the header and footer strings, to mark them as comments. Default: '#', as expected by e.g. numpy.loadtxt. str	Optional
encoding	Encoding used to encode the outputfile. Does not apply to output streams. If the encoding is something other than 'bytes' or 'latin1' you will not be able to load the file in NumPy versions < 1.14. Default is 'latin1'. {None, str}	Optional

Notes:

Further explanation of the fmt parameter (%[flag]width[.precision]specifier):

flags:

- : left justify

+ : Forces to precede result with + or -.

0 : Left pad the number with zeros instead of space (see width).

width:

Minimum number of characters to be printed. The value is not truncated if it has more characters.

precision:

For integer specifiers (eg. d,i,o,x), the minimum number of digits.
For e, E and f specifiers, the number of digits to print after the decimal point.
For g and G, the maximum number of significant digits.
For s, the maximum number of characters.

specifiers:

c : character

d or i : signed decimal integer

e or E : scientific notation with e or E.

f : decimal floating point

g,G : use the shorter of e,E or f

o : signed octal

s : string of characters

u : unsigned decimal integer

x,X : unsigned hexadecimal integer

This explanation of fmt is not complete, for an exhaustive specification see [R285].

NumPy.savetxt() method Example:

>>> import numpy as np
>>> x = y = z = np.arange(0.0,5.0,1.0)
>>> np.savetxt('test.out', x, delimiter=',')   # X is an array
>>> np.savetxt('test.out', (x,y,z))   # x,y,z equal sized 1D arrays
>>> np.savetxt('test.out', x, fmt='%1.4e')   # use exponential notation
>>> x

Output:

array([0., 1., 2., 3., 4.])

>>> import numpy as np
>>> x = y = z = np.arange(0.0,5.0,1.0)
>>> np.savetxt('test.out', x, delimiter=',')   # X is an array
>>> np.savetxt('test.out', (x,y,z))   # x,y,z equal sized 1D arrays
>>> np.savetxt('test.out', x, fmt='%1.4e')   # use exponential notation
>>> y

Output:

array([0., 1., 2., 3., 4.])

>>> import numpy as np
>>> x = y = z = np.arange(0.0,5.0,1.0)
>>> np.savetxt('test.out', x, delimiter=',')   # X is an array
>>> np.savetxt('test.out', (x,y,z))   # x,y,z equal sized 1D arrays
>>> np.savetxt('test.out', x, fmt='%1.4e')   # use exponential notation
>>> z

Output:

array([0., 1., 2., 3., 4.])

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