How to replace empty string with zero in comma-separated string?

Question

"8,5,,1,4,7,,,,7,,1,9,3,6,,,8,6,3,9,,2,5,4,,,,,3,2,,,7,4,1,1,,4,,6,9,,5,,,,5,,,1,,6,3,,,6,5,,,,7,4,,1,7,6,,,,8,,5,,,7,1,,3,9,"

I'm doing a programming challenge where i need to parse this sequence into my sudoku script. Need to get the above sequence into 8,5,0,1,4,7,0,0,0,7,0,1,9,3,6,0,0,8......... I tried re but without success, help is appreciated, thanks.

Answer 1

Regular expressions are often unnecessary in Python. Given string s, try:

','.join(x or '0' for x in s.split(','))

I am assuming you want to fill the blanks with 0. If you want a list of integers instead of a string, try this:

[(x and int(x)) or 0 for x in s.split(',')]

Answer 2

>>> s="8,5,,1,4,7,,,,7,,1,9,3,6,,,8,6,3,9,,2,5,4,,,,,3,2,,,7,4,1,1,,4,,6,9,,5,,,,5,,,1,,6,3,,,6,5,,,,7,4,,1,7,6,,,,8,,5,,,7,1,,3,9,"
>>> s=s.split(",")
>>> for n,i in enumerate(s):
...     if i=="" : s[n]=0
...
>>> s
['8', '5', 0, '1', '4', '7', 0, 0, 0, '7', 0, '1', '9', '3', '6', 0, 0, '8', '6', '3', '9', 0, '2', '5', '4', 0, 0, 0, 0, '3', '2', 0, 0, '7', '4', '1', '1', 0, '4', 0, '6', '9', 0, '5', 0, 0, 0, '5', 0, 0, '1', 0, '6', '3', 0, 0, '6', '5', 0, 0, 0, '7', '4', 0, '1', '7', '6', 0, 0, 0, '8', 0, '5', 0, 0, '7', '1', 0, '3', '9', 0]
>>>

Answer 3

You could use

[(int(x) if x else 0) for x in data.split(',')]

data.split(',') splits the string into a list. It splits on the comma character:

['8', '5', '', '1', '4', '7', '', '', '', ...]

The expression

(int(x) if x else 0)

returns int(x) if x is True, 0 if x is False. Note that the empty string is False.

Answer 4

s = "8,5,,1,4,7,,,,7,,1,9,3,6,,,8,6,3,9,,2,5,4,,,,,3,2,,,7,4,1,1,,4,,6,9,,5,,,,5,,,1,,6,3,,,6,5,,,,7,4,,1,7,6,,,,8,,5,,,7,1,,3,9,"
s = re.sub('((?<=,)|^)(?=,|$)', '0', s)
print s

Prints:

8,5,0,1,4,7,0,0,0,7,0,1,9,3,6,0,0,8,6,3,9,0,2,5,4,0,0,0,0,3,2,0,0,7,4,1,1,0,4,0,6,9,0,5,0,0,0,5,0,0,1,0,6,3,0,0,6,5,0,0,0,7,4,0,1,7,6,0,0,0,8,0,5,0,0,7,1,0,3,9,0

Answer 5

Simplest I can think of is

[int(x or 0) for x in s.split(',')]

or

[int('0'+x) for x in s.split(',')]

Answer 6

My solution uses map,lambda, and split. The final code looks like this:

sudoku_string = "1,2,3,,4,5,,6"
output_string = map(lambda x: '0' if x=='' else x, sudoku_string.split(","))

If you want the output as a list (i.e. [1,2,3,0,4,5,0,6]), then use

output_list = map(lambda x: 0 if x=='' else int(x), sudoku_string.split(",")

The commands map and lambda are very useful. map takes in a function and a list (really an iterable, but that's another story), and applies the function to every element of this list. So

def plus_one(x):
    return x+1
map(plus_one, [1,2,3,4])

returns [2,3,4,5]. lambda is a way to quickly define functions, so we can write plus_one as

lambda x: x+1

Lastly, split takes a string and creates a list by 'splitting' the string by the argument you pass. So "1 2 3 4".split(" ") yields [1,2,3,4].