Splitting a list

[Ian Sparks]

string.split() is very useful, but what if I want to split a list of integers on some element value?

e.g. :

l = [1,2,3,-1,4,5,-1,8,9]
l.split(-1)
[[1,2,3],[4,5],[8,9]]
Here's my hideous first pass :
[[int(z) for z in x.split(',') if z] for x in ','.join([str(a) for a in l]).split('-1')]
[[1, 2, 3], [4, 5], [8, 9]]

When I see code like that I just know I've missed something obvious....

[Elaine Jackson]

def indices(x,y):
if y in x:
i = x.index(y)
j = i+1
return [i]+[z+j for z in indices(x[j:],y)]
return []

def listSplit(x,y):
z = [-1] + indices(x,y) + [len(x)]
return [x[z[i]+1:z[i+1]] for i in range(len(z)-1)]
"Ian Sparks" <Ia********@etr ials.com> wrote in message
news:ma******** *************** *************** @python.org...
string.split() is very useful, but what if I want to split a list of integers on
some element value?

e.g. :

l = [1,2,3,-1,4,5,-1,8,9]
l.split(-1)
[[1,2,3],[4,5],[8,9]]
Here's my hideous first pass :
[[int(z) for z in x.split(',') if z] for x in ','.join([str(a) for a in l]).split('-1')] [[1, 2, 3], [4, 5], [8, 9]]

When I see code like that I just know I've missed something obvious....

[Andrea Griffini]

On Tue, 31 Aug 2004 09:54:17 -0400, "Ian Sparks"
<Ia********@etr ials.com> wrote:

string.split () is very useful, but what if I want to split a list of integers on some element value?

Here are a few early-morning attempts :-)

def lsplit(L,sep):
try:
i = L.index(sep)
return [L[:i]] + lsplit(L[i+1:],sep)
except ValueError:
return [L]

def lsplit2(L,sep):
i = 0
res = []
while True:
try:
j = L.index(sep,i)
res.append(L[i:j])
i = j+1
except ValueError:
res.append(L[i:])
break
return res

def lsplit3(L,sep):
i = 0
while True:
try:
j = L.index(sep,i)
yield L[i:j]
i = j+1
except ValueError:
yield L[i:]
break
HTH
Andrea

[Martin DeMello]

Ian Sparks <Ia********@etr ials.com> wrote:

string.split() is very useful, but what if I want to split a list of integers on some element value?

e.g. :

l = [1,2,3,-1,4,5,-1,8,9]
l.split(-1)
[[1,2,3],[4,5],[8,9]]

reduce (lambda a, i: i == elem and (a + [[]]) or (a[:-1] + [a[-1]+[i]]),
l, [[]])

martin

[Alex Martelli]

Ian Sparks <Ia********@etr ials.com> wrote:

string.split() is very useful, but what if I want to split a list of integers on some element value?
e.g. :

l = [1,2,3,-1,4,5,-1,8,9]
l.split(-1)
[[1,2,3],[4,5],[8,9]]
Here's my hideous first pass :
[[int(z) for z in x.split(',') if z] for x in ','.join([str(a) for a in l]).split('-1')] [[1, 2, 3], [4, 5], [8, 9]]
When I see code like that I just know I've missed something obvious....

I think a simple generator might serve you well:

def isplit(seq, separator):
result = []
for item in seq:
if item == separator:
yield result
result = []
else:
result.append(i tem)
yield result

example use:

list(isplit([1,2,3,-1,4,5,-1,8,9], -1))

[[1, 2, 3], [4, 5], [8, 9]]

Note that, the way isplit is coded, seq can be any iterable, not just a
list. You may not need this little extra generality, but it can't
hurt...
Alex