split a list based on a predicate

[Rajanikanth Jammalamadaka]

Hi!

Is there a functional way to do this?

I have an array [0,1,2,3,0,1,2,2,3] and I want the first chunk of
non-decreasing values from this array (eg: In this case I want
[0,1,2,3])

Thanks,

Rajanikanth

 

[bearophileHUGS]

Rajanikanth Jammalamadaka:

Is there a functional way to do this?
I have an array [0,1,2,3,0,1,2,2,3] and I want the first chunk of
non-decreasing values from this array (eg: In this case I want
[0,1,2,3])

In Python sometimes the best way to write the code isn't functional,
this is readable code:

s = [3,1,2,3,0,1,2,2,3,3,2]

it = iter(s)
prec = it.next() #fix this if it can be empty
groups = [[prec]]
for x in it:
if x < prec:
groups.append([])
groups[-1].append(x)
prec = x
print groups

Output:
[[3], [1, 2, 3], [0, 1, 2, 2, 3, 3], [2]]

If you want more fancy code you may use something like this:

class Infinite:
def __cmp__(self, other):
return 0 if isinstance(other, Infinite) else 1
infinite = Infinite()

it = iter(s)
prec = infinite
groups = []
for x in it:
if x < prec:
groups.append([])
groups[-1].append(x)
prec = x
print groups

If you really want functional code you may try to use groupby().

bye,
bearophile

 

[beginner]

Hi,

Hi!

Is there a functional way to do this?

I have an array [0,1,2,3,0,1,2,2,3] and I want the first chunk of
non-decreasing values from this array (eg: In this case I want
[0,1,2,3])

Thanks,

Rajanikanth

Here is an idea. It is not the most efficient code!

def combine(l, a):
if not l or l[-1]<a: l.append(a)
return l

reduce(combine, [0,1,2,3,0,1,2,2,3], [])

best regards,
beginner

 

[Rajanikanth Jammalamadaka]

Thanks for all of your replies.

Rajanikanth

Hi,

Hi!

Is there a functional way to do this?

I have an array [0,1,2,3,0,1,2,2,3] and I want the first chunk of
non-decreasing values from this array (eg: In this case I want
[0,1,2,3])

Thanks,

Rajanikanth

Here is an idea. It is not the most efficient code!

def combine(l, a):
if not l or l[-1]<a: l.append(a)
return l

reduce(combine, [0,1,2,3,0,1,2,2,3], [])

best regards,
beginner