How to group in Python?

[tcl76]

hi,

assume data looks like this:
cell Bit
0 1
1 X
2 1
3 0
4 X
5 X
6 X
7 X
8 1
9 X
10 0
11 0
12 X
13 X
14 1
15 1

And i want to group 4 bits into each group such as:
ROW1=01X1
ROW2=XXXX
ROW3=00X1
ROW4=11XX

how to do this?

thanks

[TrustyTony]

Not so simple, but here is my solution based on simplified grouper as I used in my Sudoku post resently. More complete solution for grouping can be found in manual of itertools, using izip_longest.

def grouper(n, iterable): return zip(*((iter(iterable),) * n))

data = """cell Bit
0 1
1 X
2 1
3 0
4 X
5 X
6 X
7 X
8 1
9 X
10 0
11 0
12 X
13 X
14 1
15 1"""

bits = zip(*(row.split() for row in (data.splitlines()[1:])))
## let's check that we dropped the header and transposed with zip(*) properly
print bits
## bits needed to reverse still and we must reverse the result back
## let's do it by reversed and by taking slice of step -1 slice to demonstrate two ways
bits = list(grouper(4, reversed(bits[1])))[::-1]
print('\n'.join('ROW{index}={line}'.format(index=index+1, line=''.join(line)) for index,line in enumerate(bits)))

[tcl76]

wow.. this is really complex. :)
i got this error after executing the code:
>>>
[('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14', '15'), ('1', 'X', '1', '0', 'X', 'X', 'X', 'X', '1', 'X', '0', '0', 'X', 'X', '1', '1')]
Traceback (most recent call last):
File "C:\Python25\myscript\group\group.py", line 27, in <module>
print('\n'.join('ROW{index}={line}'.format(index=index+1, line=''.join(line)) for index,line in enumerate(bits)))
File "C:\Python25\myscript\group\group.py", line 27, in <genexpr>
print('\n'.join('ROW{index}={line}'.format(index=index+1, line=''.join(line)) for index,line in enumerate(bits)))
AttributeError: 'str' object has no attribute 'format'
>>>

pls advise.

[griswolf]

AttributeError: 'str' object has no attribute 'format'
You are using an older version of Python. You can replace line 27 with this: print('\n'.join('ROW%d=%s'%(index+1,''.join(line)) for index,line in enumerate(bits)))

[tcl76]

excellent this works!! :)

[tcl76]

suppose data is inside a file (eg test.txt). modified the code to be:

def grouper(n, iterable): return zip(*((iter(iterable),) * n))

f=open('test.txt')
for line in f:

    bits = zip(*(row.split() for row in (line.splitlines()[1:])))
    ## let's check that we dropped the header and transposed with zip(*) properly
    print bits
    ## bits needed to reverse still and we must reverse the result back
    ## let's do it by reversed and by taking slice of step -1 slice to demonstrate two ways
    bits = list(grouper(4, reversed(bits[1])))[::-1]
    print('\n'.join('ROW%d=%s'%(index+1,''.join(line)) for index,line in enumerate(bits)))

but getting traceback error:
>>>
[]
Traceback (most recent call last):
File "C:/Python25/myscript/group/group4.py", line 11, in <module>
bits = list(grouper(4, reversed(bits[1])))[::-1]
IndexError: list index out of range
>>>

pls advise. tq

[TrustyTony]

I don't understand why you left the splitlines even you have line ready. Try by replacing line.splitlines() with open('test.txt').

[tcl76]

do you mean:
bits = zip(*(row.split() for row in (line.open('test.txt')[1:])))

[TrustyTony]

Like this:

def grouper(n, iterable): return zip(*((iter(iterable),) * n))

f = open('test.txt')
next(f) # drop header
bits = zip(*(row.strip().split() for row in f))
bits = list(grouper(4, reversed(bits[1])))[::-1]
print('\n'.join('ROW%d=%s'%(index+1,''.join(line)) for index,line in enumerate(bits)))

[tcl76]

i'm getting next(f) not defined. i'm using Python 2.5 and Win XP.

Traceback (most recent call last):
File "C:\Python25\myscript\group\group4.py", line 19, in <module>
next(f) # drop header
NameError: name 'next' is not defined

[griswolf]

So if you wanted to get lines from an open file, what would you do in your version of Python? Hint: look up getlines() Seems to me as if you could do a little better at actually thinking about the program and what the error message is telling you.

[TrustyTony]

Why to use so old Python? Use f.next() syntax. Preferably update to Python 2.7.1.

[tcl76]

ha..ha... i guess Python 2.5 is more stable. :)
i guess getline is the equalvalent of next. there is also readline.