Explaining the Schwartzian Transform

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1. #!/usr/bin/env perl  
2.   
3. # what is a schwartzian transform?  
4.   
5. # http://en.wikipedia.org/wiki/Schwartzian_transform  
6.   
7. use feature qw{ say } ;   
8.   
9. # notice how all of these are not in any order?  
10.   
11. my @tedx_feeds = qw{  
12.     tedx  
13.     tedxboston  
14.     tedxindianapolis  
15.     tedxiu  
16.     tedxpurdueu  
17.     tedxlafayette  
18.     tedxohiostateu  
19.     tedxpsu  
20.     tedxuiowa  
21.     } ;  
22.   
23. # we'll read this backwards.   
24. my @sorted =   
25.     map { $_->[0] }   
26.     # ... and then we just use the words, jettisoning  
27.     # the lengths and creating the final array.  
28.   
29.     sort { $a->[1] <=> $b->[1] }  
30.     # ... which we sort numerically by the length  
31.       
32.     map { [ $_ , length $_ ] }   
33.     # ... becomes an array of arrays, being all  
34.     # the words and their lengths, starting   
35.     # with [ 'tedx' , 4 ] ...  
36.   
37.     @tedx_feeds ; # the array in unsorted order ...  
38.   
39. # Start here and go up <-----------------<<<<<  
40.   
41. say join "\n" , @sorted ;  
42.   
43. # output looks like:  
44. # tedx  
45. # tedxiu  
46. # tedxpsu  
47. # tedxuiowa  
48. # tedxboston  
49. # tedxpurdueu  
50. # tedxlafayette  
51. # tedxohiostateu  
52. # tedxindianapolis  

#!/usr/bin/env perl

# what is a schwartzian transform?

# http://en.wikipedia.org/wiki/Schwartzian_transform

use feature qw{ say } ; 

# notice how all of these are not in any order?

my @tedx_feeds = qw{
    tedx
    tedxboston
    tedxindianapolis
    tedxiu
    tedxpurdueu
    tedxlafayette
    tedxohiostateu
    tedxpsu
    tedxuiowa
    } ;

# we'll read this backwards. 
my @sorted = 
    map { $_->[0] } 
    # ... and then we just use the words, jettisoning
    # the lengths and creating the final array.

    sort { $a->[1] <=> $b->[1] }
    # ... which we sort numerically by the length
    
    map { [ $_ , length $_ ] } 
    # ... becomes an array of arrays, being all
    # the words and their lengths, starting 
    # with [ 'tedx' , 4 ] ...

    @tedx_feeds ; # the array in unsorted order ...

# Start here and go up <-----------------<<<<<

say join "\n" , @sorted ;

# output looks like:
# tedx
# tedxiu
# tedxpsu
# tedxuiowa
# tedxboston
# tedxpurdueu
# tedxlafayette
# tedxohiostateu
# tedxindianapolis

It took me quite a long time to get the Transform, and the use of map and grep. But they aren't hard. Once you get them, you'll use them everywhere. Maybe too much....