Is there a way to subtract 3 from every digit of a number?

[C W]

I got it to work! I defined a separate function, and put it into
df['col_1'].apply().

Not the most elegant, but it worked. I'm also curious how people on this
mailing list would do it.

Cheers!

On Sun, Feb 21, 2021 at 9:21 AM C W <tmrsg11 at gmail.com> wrote:

> I do want to follow up, if I may. In Ming's example,
>
> a = 2342
> b = int("".join(map(lambda x: str((int(x)-3)%10) ,list(str(a)))))
>
> What's the best approach to apply to a dataframe column, rather than just
> one value?  Here's my attempt using df[col_1''].apply(),
> df['col_1'].apply(lambda:a int("".join(map(lambda x: str((int(x)-3)%10)
> ,list(str(a))))))
>
> Thanks!
>
> On Sun, Feb 21, 2021 at 9:12 AM C W <tmrsg11 at gmail.com> wrote:
>
>> Thanks so much everyone, I appreciate it!
>>
>> Ming, your solution is awesome. More importantly, very clear explanations
>> on how and why. So, I appreciate that.
>>
>> Thanks again, cheers!
>>
>> Mike
>>
>> On Sun, Feb 21, 2021 at 12:08 AM <2QdxY4RzWzUUiLuE at potatochowder.com>
>> wrote:
>>
>>> On 2021-02-20 at 20:49:15 -0800,
>>> Dan Stromberg <drsalists at gmail.com> wrote:
>>>
>>> > On Sat, Feb 20, 2021 at 7:13 PM Ming <ming at pgp.cool> wrote:
>>> >
>>> > > I just wrote a very short code can fulfill your needs:
>>> > >
>>> > > a = 2342
>>> > > b = int("".join(map(lambda x: str((int(x)-3)%10) ,list(str(a)))))
>>> > >
>>> > I tend to favor plenty of temporary variables with descriptive names,
>>> but
>>> > this is indeed short.
>>> >
>>> > Apart from that, you may find that using a generator expression is
>>> shorter
>>> > and clearer than map+lambda.  It should allow to additionally
>>> eliminate the
>>> > list conversion.
>>> >
>>> > So in the terse form you've got there, it'd be more like:
>>> > b =  int(''.join(str((int(x) - 3) % 10) for x in str(a))
>>> >
>>> > But in real life, I'd try to use descriptive variable names for some
>>> of the
>>> > subexpressions in that.  This makes reading and debugging simpler,
>>> which is
>>> > important because the maintenance phase of software is almost always
>>> much
>>> > longer and costly than the development phase.  And although you could
>>> do a
>>> > generator expression for each of the different parts of (int(x) - 3) %
>>> 10,
>>> > I kinda like having a named function for just that piece.
>>> >
>>> > So maybe:
>>> >   def rot_3(character):
>>> >       """Convert to int, subtract 3 and mod 10."""
>>> >       digit = int(character)
>>> >       assert 0 <= digit <= 9
>>> >       return (digit - 3) % 10
>>> >
>>> >
>>> >   def descriptive_minus_three_caesar(input_number):
>>> >       """Convert to a -3 caesar cypher on an integer."""
>>> >       string_number = str(input_number)
>>> >       rotated_digits = (rot_3(character) for character in
>>> string_number)
>>> >       output_string = ''.join(str(digit) for digit in rotated_digits)
>>> >       output_number = int(output_string)
>>> >       return output_number
>>>
>>> >>> descriptive_minus_three_caesar('38')
>>> 5
>>>
>>> The problem is underspecified, and the examples are lacking, but based
>>> on the phrase "each digit" and the examples that contain a 3, I'd prefer
>>> to see "38" become "05."
>>> --
>>> https://mail.python.org/mailman/listinfo/python-list
>>>
>>