Dict Comprehension ?

[Ernst-Ludwig Brust]

Given 2 Number-Lists say l0 and l1,
count the various positiv differences between the 2 lists

the following part works:

dif=[abs(x-y) for x in l0 for y in l1]
da={}
for d in dif: da[d]=da.get(d,0)+1

i wonder, if there is a way, to avoid the list dif

Ernst-Ludwig Brust

 

[bearophileHUGS]

Ernst-Ludwig Brust:

Given 2 Number-Lists say l0 and l1,
count the various positiv differences between the 2 lists
...
i wonder, if there is a way, to avoid the list dif

Instead of creating the list (array) dif, you can create a lazy
iterator. Then you can fed it to a set.

Bye,
bearophile

 

[pruebauno]

Given 2 Number-Lists say l0 and l1,
count the various positiv differences between the 2 lists

the following part works:

dif=[abs(x-y) for x in l0 for y in l1]
da={}
for d in dif: da[d]=da.get(d,0)+1

i wonder, if there is a way, to avoid the list dif

Ernst-Ludwig Brust

from collections import defaultdict
da=defaultdict(int)
for x in [10]:
for y in [11]:
da[abs(x-y)]+=1

 

[Ernst-Ludwig Brust]

Instead of creating the list (array) dif, you can create a lazy
iterator. Then you can fed it to a set.

Thangs,
this idea is not only less storage-consuming but even faster
than the "List-Version".
But, i used the idea of pruebauno,
as this is faster.

Ernst-Ludwig Brust

 

[Ernst-Ludwig Brust]

So, generator expressions can be a powerful way to clarify the purpose
of a section of code. They can be over-used, though: don't use them
unless they actually *do* clarify the code; sometimes an explicit
looping construct is clearer.

Thangs,
my opinion was, that "one-statement-constructions" are
much faster then f.e. explicit loops.
But,
now i know, with Python, this is not allways true.

Ernst-Ludwig Brust

 

[Ernst-Ludwig Brust]

from collections import defaultdict
da=defaultdict(int)
for x in [10]:
for y in [11]:
da[abs(x-y)]+=1

Thangs,
collections are a real good idea.
I will use this version.

Ernsst-Ludwwig Brust