Hi, I wrote a C++ class that implements an n dimensional histogram in
C++, using stl maps and vectors. I want to code this up now in Python
and would like some input from this group.
The C++ class was VERY simple..
std::map<std::v ector<unsigned short>, unsigned long> histo;
Say for example I want a 3D histogram then std::vector<uns igned short>
would contains
the x, y, and z points in space and the unsigned long is the number of
counts.
If I want to know the value at a specific point in space I pass in a
vector [3,2,1] and if
it is found in the map then the count is returned other wise zero is
returned.
If I want to increment a count then histo[vector]++ will either set the
count to 1 or increment
the count if it is found...
So as you can see this is a very simple way to implement a multi
dimensional sparse histogram.
I'm thinking that in python this must also be as simple as a
dictionary, where the key is the vector x,y,z and the value is the
count.
My python is ok, but not the best and I was hoping some one here might
want to help me out?
This doesn't work for example...
histo = {[0,0,0]:1, [0,0,1]:2}
Would indicate that there is one sample at 0,0,0 and two samples at
0,0,1
but python tells me TypeError: list objects are unhashable
So any suggestions would be welcome.
TIA. 12 2855
KraftDiner <bo*******@yaho o.com> wrote:
... histo = {[0,0,0]:1, [0,0,1]:2} Would indicate that there is one sample at 0,0,0 and two samples at 0,0,1 but python tells me TypeError: list objects are unhashable
So any suggestions would be welcome.
Use tuples, not lists, as your keys:
histo = {(0,0,0):1, (0,0,1):2}
Alex
Cool.
Ok so my histogram class had two methods 1) To increment a point and 2)
to get the point.
def class histo:
def __init__(self):
histo = {}
def update(point):
'''searches the dictionary for point and if it exists increment the
value.
if it doesn't exist set the value to 1'''
def get(point):
return self.histo[point]
I'm not sure how to code up the update routine...
On Wed, 2006-02-01 at 19:06 -0800, KraftDiner wrote: Cool. Ok so my histogram class had two methods 1) To increment a point and 2) to get the point.
def class histo: def __init__(self): histo = {} def update(point): '''searches the dictionary for point and if it exists increment the value. if it doesn't exist set the value to 1'''
def get(point): return self.histo[point]
I'm not sure how to code up the update routine...
-- http://mail.python.org/mailman/listinfo/python-list
def update(point);
if histo.get(point ) != None:
histo[point] = histo[point] + 1
Regards,
John
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
KraftDiner <bo*******@yaho o.com> wrote: Cool. Ok so my histogram class had two methods 1) To increment a point and 2) to get the point.
def class histo: def __init__(self): histo = {} def update(point): '''searches the dictionary for point and if it exists increment the value. if it doesn't exist set the value to 1'''
def update(self, point):
self.histo[point] = 1 + self.histo.get( point, 0) def get(point):
def (self, point):
actually.
return self.histo[point]
I'm not sure how to code up the update routine...
See above.
Alex
The dictionary is sorted by the point key.
Is there a way to sort the dictionary by the value?
Seems to me this goes against the purpose of a dictionary but....
thats what I need to do..
KraftDiner wrote: The dictionary is sorted by the point key. Is there a way to sort the dictionary by the value? Seems to me this goes against the purpose of a dictionary but.... thats what I need to do..
Well, it's probably not all that efficient, but it is simple code:
sortedList = [(v, k) for k, v in self.histo.item s()]
sortedList.sort ()
Should do it...
-Kirk McDonald
Ok so this is nice.. Just one thing.. When you try to get a value from
a dictionary
and it isn't found in the dictionary things go bad...
Take this for example:
class histogram(objec t):
def __init__(self):
self.histo = {}
def update(self, point):
if self.histo.get( point) != None:
self.histo[point] = self.histo[point] + 1
else:
self.histo[point] = 1
def get(self, point):
return self.histo[point]
hist = histogram()
hist.update((0, 0,0))
hist.update((0, 0,1))
hist.update((0, 0,1))
hist.get((0,0,0 ))
hist.get((0,0,1 ))
hist.get((0,0,2 ))
spews out this error:
Traceback (most recent call last):
File "histogram. py", line 21, in ?
hist.get((0,0,2 ))
File "histogram. py", line 12, in get
return self.histo[point]
KeyError: (0, 0, 2)
KraftDiner wrote: Ok so this is nice.. Just one thing.. When you try to get a value from a dictionary and it isn't found in the dictionary things go bad...
Take this for example:
class histogram(objec t): def __init__(self): self.histo = {}
def update(self, point): if self.histo.get( point) != None: self.histo[point] = self.histo[point] + 1 else: self.histo[point] = 1
def get(self, point): return self.histo[point]
hist = histogram() hist.update((0, 0,0)) hist.update((0, 0,1)) hist.update((0, 0,1)) hist.get((0,0,0 )) hist.get((0,0,1 )) hist.get((0,0,2 ))
spews out this error:
Traceback (most recent call last): File "histogram. py", line 21, in ? hist.get((0,0,2 )) File "histogram. py", line 12, in get return self.histo[point] KeyError: (0, 0, 2)
Try this:
class histogram(objec t):
def __init__(self):
self.histo = {}
def update(self, point):
self.histo[point] = self.histo.get( point, 0) + 1
def get(self, point):
return self.histo.get( point, 0)
dict.get's default return value is your friend.
-Kirk McDonald
Hi
you can use has_key() to check whether
the particular value is in the key set or not. a = {} a[1] = 22 a[2] = 33 a
{1: 22, 2: 33} a.has_key(3)
False a.has_key(1)
True
-raj
KraftDiner wrote: Ok so this is nice.. Just one thing.. When you try to get a value from a dictionary and it isn't found in the dictionary things go bad...
Take this for example:
class histogram(objec t): def __init__(self): self.histo = {}
def update(self, point): if self.histo.get( point) != None: self.histo[point] = self.histo[point] + 1 else: self.histo[point] = 1
def get(self, point): return self.histo[point]
hist = histogram() hist.update((0, 0,0)) hist.update((0, 0,1)) hist.update((0, 0,1)) hist.get((0,0,0 )) hist.get((0,0,1 )) hist.get((0,0,2 ))
spews out this error:
Traceback (most recent call last): File "histogram. py", line 21, in ? hist.get((0,0,2 )) File "histogram. py", line 12, in get return self.histo[point] KeyError: (0, 0, 2) This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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