Concatenate string list to number list to form title - Logic needed.

Terry Reedy tjreedy at udel.edu
Mon Dec 16 21:23:14 CET 2013


On 12/16/2013 12:43 PM, Mark Lawrence wrote:
> On 16/12/2013 17:16, Ravi Prabakaran wrote:
>> Hi,
>> I'm completely new to python. I just need simple logic to get output
>> without any loops.
>> I have list of string

The remainder of your description and example imply that this must be a 
sequence of exactly two strings. In other words, 'list' is both too 
specific as to class and not specific enough as to length.

 >> and list of list of numbers.

While this must be an iterable of sequences of exactly 4 numbers.

>> Each string should be concatenated with every third and fourth values
>> to generate proper titles in list of strings.
>>
>> t = ['Start','End']
>> a = [[1,2,3,4],
>>       [5,6,7,8]]
>>
>> Expected Result : ( list of strings )
>>
>> ['Start - 3 , End - 4',
>>   'Start - 7 , End - 8']
>>
>> Note : First 2 values from each list should be ignored.
>>
>> Could anyone please guide me with best solution without loops ?

If the length of the iterable of sequences is not fixed, a loop of some 
sort is needed.

> I've no idea what your definition of "best" is but this works.
>
> strings = ['{} - {} , {} - {}'.format(t[0], b[-2], t[1], b[-1]) for b in a]

Very nice. The following use the format mini language to do the 
indexing, avoiding passing the args twice each.

strings = ['{0[0]} - {1[2]} , {0[1]} - {1[3]}'.format(t, b) for b in a]

form = '{src[0]} - {val[2]} , {src[1]} - {val[3]}'
strings = [form.format(src=t, val=b) for b in a]

The first should be faster, but may be less readable. Note that '-2' and 
'-1' do not work as int indexes in the field names because they would be 
interpreted as string keys rather than integers.

-- 
Terry Jan Reedy




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