Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris
 
PerlMonks  

Re^3: Sorting dates with the Schwartzian Transform

by johngg (Abbot)
on Aug 03, 2011 at 22:42 UTC ( #918400=note: print w/replies, xml ) Need Help??


in reply to Re^2: Sorting dates with the Schwartzian Transform
in thread Sorting dates with the Schwartzian Transform

... how I would know that the map {} sort {} map {} would be executed in reverse order, but I didn't find it. Any clues?

Both map and sort take a list (which is on the RHS), do some transformation of it then return the transformed list (to the LHS).

my @mapped = map { # some transform code } @unmapped; my @sorted = sort { # sorting code } @unsorted;

The ST code is just an extension of this right-to-left pattern:

  • the first map extracts the sorted dates in the original DD-MM-YYYY format and assigns to the @dates array on the LHS of the assignment operator (=);

  • but it can't do that before the sort has evaluated, sorting the items;

  • which in turn can't do any sorting before the bottom (or rightmost) map has transformed some dates into something sort can work with, taking its raw material from the rightmost part of the expression which is the original, unsorted @dates array.

I hope this makes things a bit clearer.

Cheers,

JohnGG

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://918400]
help
Chatterbox?
[karlgoethebier]: Hi mario
[marioroy]: Hi karlgoethebier.
[karlgoethebier]: "Long time No See" ;-)
[marioroy]: Yes. I've been working on MCE and MCE::Shared. These are completed and released. MCE 1.830 and MCE::Shared 1.831. Saw the LWP::Simple and P::FM thread and thought to help out.
[marioroy]: Today, wanted to revisit running parallel Re: Crash with ForkManager on Windows. I tried running on Cygwin for comparison.
[marioroy]: Running parallel on Cygwin feels like running on Unix ;-)

How do I use this? | Other CB clients
Other Users?
Others scrutinizing the Monastery: (7)
As of 2017-09-23 15:56 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    During the recent solar eclipse, I:









    Results (272 votes). Check out past polls.

    Notices?