Split array by rows

Question

I have a very basic problem.I have wrote a code which open a .txt file which contain a numbers 1 2 3 4 5 6 7 8 9.Then it square all of it and write to other file. Right now I want to add to this code procedure which split all of this numbers in rows and rewrite,like this:

1 4 9
16 25 36
49 64 81

My code already:

n=[]
dane = open("num.txt", "r")
for i in dane:
 i = i.replace('\n','')
 for j in i.split(' '):
 j = int(j)
 j = j**2
 n.append(j)
nowy = open("newnum.txt","w")
nowy.write(str(n))
nowy.close()

• Bhargav Rao: So what is the problem with the code?
• Avinash Raj: how your actual input looks like?

Answer 1

The code you have written works fine expect for the writing part. For which you need to change the last three lines of code as

nowy = open("newnum.txt","w")
for i in range(0,len(n),3):
 nowy.write("{} {} {}\n".format(n[i],n[i+1],n[i+2]))
nowy.close()

The for loop can be explained as,

• loop through the list n that you have generated 3 at a time by using the third argument to the range function which is called step.
• write out the values three at a time into the file, terminated by the newline character

The output after changing the lines of code is as expected

1 4 9
16 25 36
49 64 81

Ref:

• format
• range

• Bhargav Rao: @wiedzminYo All the best :)

Answer 2

As a complement to @Bhargav's answer, according to the doc "[a] possible idiom for clustering a data series into n-length groups [is] using zip(*[iter(s)]*n)"

You can use the star to unpack a list/tuple as arguments to format function call too.

All this will lead to a more Pythonic (or, rather crypto-Pythonic ?) version of the writing part:

with open("newnum.txt","w") as nowy:
 for sublist in zip(*[iter(n)]*3):
 nowy.write("{} {} {}\n".format(*sublist))

Please note the use of a context manager (with statement) to ensure proper closing of the file in all cases when exiting from the block. As other changes would be subject to discussion, that later is a must -- and you should definitively take the habit of using it
_{(BTW, have you noticed you never closed the dane file? A simple mistake that would have been avoided by the use of a context manager to manage that resource...)}

Answer 3

You can try this:

strNew = ''
dane = open("num.txt", "r")
row = 0
for i in dane:
 i = i.replace('\n','')
 for j in i.split(' '):
 row += 1
 j = int(j)
 j = j**2
 if (row % 3) == 0:
 strNew += str(j)+'\n'
 else:
 strNew += str(j) + ' ' # it can be ' ' or '\t'
nowy = open("newnum.txt","w")
nowy.write(strNew)
nowy.close()

The result is:

1 4 9
16 25 36
49 64 81

Answer 4

n=[]
dane = open("num.txt", "r")
for i in dane:
 i = i.replace('\n','')
 for j in i.split(' '):
 j = int(j)
 j = j**2
 # new code added
 # why str(j)? Because array in Python can only have one type of element such as string, int, etc. as opposed to tuple that can have multiple type in itself. I appended string because I wanna append \n at the end of each step(in outer loop I mean)
 n.append(str(j))
 # new code added
 n.append("\n")
nowy = open("newnum.txt","w")
nowy.write(str(n))
nowy.close()

• PM 2Ring: "array in Python can only have one type of element". n is a Python list; Python doesn't have a native array type (although a Python list is implemented in CPython as an array of pointers). The elements of a Python list do not have to be of the same type. However, it's generally considered good programing style to avoid mixing types in a list (apart from special values like None), but that's a guideline, not a hard & fast rule.