How to read numbers from file in Python?
I'd like to read numbers from file into two dimensional array.
File contents:
- line containing w, h
- h lines containing w integers separated with space
For example:
4 3
1 2 3 4
2 3 4 5
6 7 8 9
Assuming you don't have extraneous whitespace:
with open('file') as f:
w, h = [int(x) for x in next(f).split()] # read first line
array = []
for line in f: # read rest of lines
array.append([int(x) for x in line.split()])
You could condense the last for loop into a nested list comprehension:
with open('file') as f:
w, h = [int(x) for x in next(f).split()]
array = [[int(x) for x in line.split()] for line in f]
To me this kind of seemingly simple problem is what Python is all about. Especially if you're coming from a language like C++, where simple text parsing can be a pain in the butt, you'll really appreciate the functionally unit-wise solution that python can give you. I'd keep it really simple with a couple of built-in functions and some generator expressions.
You'll need open(name, mode), myfile.readlines(), mystring.split(), int(myval), and then you'll probably want to use a couple of generators to put them all together in a pythonic way.
# This opens a handle to your file, in 'r' read mode
file_handle = open('mynumbers.txt', 'r')
# Read in all the lines of your file into a list of lines
lines_list = file_handle.readlines()
# Extract dimensions from first line. Cast values to integers from strings.
cols, rows = (int(val) for val in lines_list[0].split())
# Do a double-nested list comprehension to get the rest of the data into your matrix
my_data = [[int(val) for val in line.split()] for line in lines_list[1:]]
Look up generator expressions here. They can really simplify your code into discrete functional units! Imagine doing the same thing in 4 lines in C++... It would be a monster. Especially the list generators, when I was I C++ guy I always wished I had something like that, and I'd often end up building custom functions to construct each kind of array I wanted.
Not sure why do you need w,h. If these values are actually required and mean that only specified number of rows and cols should be read than you can try the following:
output = []
with open(r'c:\file.txt', 'r') as f:
w, h = map(int, f.readline().split())
tmp = []
for i, line in enumerate(f):
if i == h:
break
tmp.append(map(int, line.split()[:w]))
output.append(tmp)
is working with both python2(e.g. Python 2.7.10) and python3(e.g. Python 3.6.4)
with open('in.txt') as f:
rows,cols=np.fromfile(f, dtype=int, count=2, sep=" ")
data = np.fromfile(f, dtype=int, count=cols*rows, sep=" ").reshape((rows,cols))
another way:
is working with both python2(e.g. Python 2.7.10) and python3(e.g. Python 3.6.4),
as well for complex matrices see the example below (only change int to complex)
with open('in.txt') as f:
data = []
cols,rows=list(map(int, f.readline().split()))
for i in range(0, rows):
data.append(list(map(int, f.readline().split()[:cols])))
print (data)
I updated the code, this method is working for any number of matrices and any kind of matrices(int,complex,float) in the initial in.txt file.
This program yields matrix multiplication as an application. Is working with python2, in order to work with python3 make the following changes
print to print()
and
print "%7g" %a[i,j], to print ("%7g" %a[i,j],end="")
the script:
import numpy as np
def printMatrix(a):
print ("Matrix["+("%d" %a.shape[0])+"]["+("%d" %a.shape[1])+"]")
rows = a.shape[0]
cols = a.shape[1]
for i in range(0,rows):
for j in range(0,cols):
print "%7g" %a[i,j],
print
print
def readMatrixFile(FileName):
rows,cols=np.fromfile(FileName, dtype=int, count=2, sep=" ")
a = np.fromfile(FileName, dtype=float, count=rows*cols, sep=" ").reshape((rows,cols))
return a
def readMatrixFileComplex(FileName):
data = []
rows,cols=list(map(int, FileName.readline().split()))
for i in range(0, rows):
data.append(list(map(complex, FileName.readline().split()[:cols])))
a = np.array(data)
return a
f = open('in.txt')
a=readMatrixFile(f)
printMatrix(a)
b=readMatrixFile(f)
printMatrix(b)
a1=readMatrixFile(f)
printMatrix(a1)
b1=readMatrixFile(f)
printMatrix(b1)
f.close()
print ("matrix multiplication")
c = np.dot(a,b)
printMatrix(c)
c1 = np.dot(a1,b1)
printMatrix(c1)
with open('complex_in.txt') as fid:
a2=readMatrixFileComplex(fid)
print(a2)
b2=readMatrixFileComplex(fid)
print(b2)
print ("complex matrix multiplication")
c2 = np.dot(a2,b2)
print(c2)
print ("real part of complex matrix")
printMatrix(c2.real)
print ("imaginary part of complex matrix")
printMatrix(c2.imag)
as input file I take in.txt:
4 4
1 1 1 1
2 4 8 16
3 9 27 81
4 16 64 256
4 3
4.02 -3.0 4.0
-13.0 19.0 -7.0
3.0 -2.0 7.0
-1.0 1.0 -1.0
3 4
1 2 -2 0
-3 4 7 2
6 0 3 1
4 2
-1 3
0 9
1 -11
4 -5
and complex_in.txt
3 4
1+1j 2+2j -2-2j 0+0j
-3-3j 4+4j 7+7j 2+2j
6+6j 0+0j 3+3j 1+1j
4 2
-1-1j 3+3j
0+0j 9+9j
1+1j -11-11j
4+4j -5-5j
and the output look like:
Matrix[4][4]
1 1 1 1
2 4 8 16
3 9 27 81
4 16 64 256
Matrix[4][3]
4.02 -3 4
-13 19 -7
3 -2 7
-1 1 -1
Matrix[3][4]
1 2 -2 0
-3 4 7 2
6 0 3 1
Matrix[4][2]
-1 3
0 9
1 -11
4 -5
matrix multiplication
Matrix[4][3]
-6.98 15 3
-35.96 70 20
-104.94 189 57
-255.92 420 96
Matrix[3][2]
-3 43
18 -60
1 -20
[[ 1.+1.j 2.+2.j -2.-2.j 0.+0.j]
[-3.-3.j 4.+4.j 7.+7.j 2.+2.j]
[ 6.+6.j 0.+0.j 3.+3.j 1.+1.j]]
[[ -1. -1.j 3. +3.j]
[ 0. +0.j 9. +9.j]
[ 1. +1.j -11.-11.j]
[ 4. +4.j -5. -5.j]]
complex matrix multiplication
[[ 0. -6.j 0. +86.j]
[ 0. +36.j 0.-120.j]
[ 0. +2.j 0. -40.j]]
real part of complex matrix
Matrix[3][2]
0 0
0 0
0 0
imaginary part of complex matrix
Matrix[3][2]
-6 86
36 -120
2 -40
The shortest I can think of is:
with open("file") as f:
(w, h), data = [int(x) for x in f.readline().split()], [int(x) for x in f.read().split()]
You can seperate (w, h) and data if it looks neater.