difference between 2 arrays

[Pierre]

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

Well, the equivalence of setdiff in matlab...

I thought a.difference(b) could work, but no : AttributeError:
'numpy.ndarray' object has no attribute 'difference'

Thanks !

 

[Diez B. Roggisch]

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

Well, the equivalence of setdiff in matlab...

I thought a.difference(b) could work, but no : AttributeError:
'numpy.ndarray' object has no attribute 'difference'

Not sure if this works with numpy-arrays, but

set(a) - set(b)

might just work if the arrays are iterable.

Diez

 

[Michel Claveau - MVP]

(envoyé via
Hi!

See the module "sets"

@-salutations

 

[Michel Claveau - MVP]

Re !

Juste pour signaler qu'il existe un newsgroup en français sur Python, qui permet de recevoir des réponses en français (donc plus complètes/détaillées).

@-salutations

 

[John Machin]

See the module "sets"

See especially the notice at the front of the current sets doc which
says "deprecated since 2.6" and the comparison down the end which
explains why the built-in set() and frozenset() are better than the
sets module. Starting now to use the sets module is not a good idea
unless the OP is stuck on using Python 2.3 .

 

[baalu aanand]

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

Well, the equivalence of setdiff in matlab...

I thought a.difference(b) could work, but no : AttributeError:
'numpy.ndarray' object has no attribute 'difference'

Thanks !

Hi,

Here I have given my logic, check whether it helps for you

a = [1,2, 3,2,5,2]
b = [1,2]
j = 0
dif = []
for i in range(len(a)) :
if a not in b:
dif.append(a)
j += 1

print dif[k]



Thanks
Baalu

 

[baalu aanand]

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

Well, the equivalence of setdiff in matlab...

I thought a.difference(b) could work, but no : AttributeError:
'numpy.ndarray' object has no attribute 'difference'

Thanks !

Hi,

Here I have given my logic, check whether it helps for you

a = [1,2, 3,2,5,2]
b = [1,2]
j = 0
dif = []
for i in range(len(a)) :
if a not in b:
dif.append(a)
j += 1

print dif

Thanks
Baalu

 

[Matthias Huening]

Pierre (19.08.2009 10:48):

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

What about set()?

>>> a = set([1,2, 3,2,5,2])
>>> b = set([1,2])
>>> a.difference(b)

set([3, 5])


Matthias

 

[David Robinow]

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

Well, the equivalence of setdiff in matlab...

I thought a.difference(b) could work, but no : AttributeError:
'numpy.ndarray' object has no attribute 'difference'

Thanks !

import numpy
a = numpy.array([1,2,3,2,5,2])
b = numpy.array([1,2])
c = list(set(a)-set(b))
# or c = numpy.array(list(set(a)-set(b))) if you want to continue w/ arrays
print c

 

[Diez B. Roggisch]

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

Well, the equivalence of setdiff in matlab...

I thought a.difference(b) could work, but no : AttributeError:
'numpy.ndarray' object has no attribute 'difference'

Thanks !

Hi,

Here I have given my logic, check whether it helps for you

a = [1,2, 3,2,5,2]
b = [1,2]
j = 0
dif = []
for i in range(len(a)) :
if a not in b:
dif.append(a)
j += 1

print dif[k]

EEEK, quadratic behavior!!

Diez

 

[Robert Kern]

Hello,

I would like to know how to find the difference (set operation)
between 2 arrays :

a = array([1,2, 3,2,5,2])
b = array([1,2])
I want a - b = [3,5]

Well, the equivalence of setdiff in matlab...

You will want to ask numpy questions on the numpy mailing list.

http://www.scipy.org/Mailing_Lists

Using set() is frequently a good option, but for large arrays, you will want to
avoid the overhead of converting to and from sets and use numpy.setdiff1d(a, b):

In [2]: a = array([1,2, 3,2,5,2])

In [3]: b = array([1,2])

In [4]: numpy.setdiff1d(a, b)
Out[4]: array([3, 5])

--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco

 

[sturlamolden]

Well, the equivalence of setdiff in matlab...

That would be numpy.setdiff1d.

 

[Jan Kaliszewski]

19-08-2009 o 10:56:20 <""Michel Claveau -

(envoyé via
Hi!

See the module "sets"

No, see the builtin set type. Module sets is deprecated (removed in Py 3.x)

 

[Michel Claveau - MVP]

(envoyé via

Hi!

Yes, the module sets is written, in doc, like "deprecated".
But:
- sets exist in Python 2.6 (& 2.5 or 2.4)
- documentation of sets (module) is better tha, documentation of set (builtin)

The best: read the documentaion of the module, and use the builtin...

@-salutations

 

[Gabriel Genellina]

En Thu, 20 Aug 2009 06:54:05 -0300, <""Michel Claveau -

Yes, the module sets is written, in doc, like "deprecated".
But:
- sets exist in Python 2.6 (& 2.5 or 2.4)
- documentation of sets (module) is better tha, documentation of set
(builtin)

The best: read the documentaion of the module, and use the builtin...

Any suggestion to improve the builtin set documentation? In what ways do
you see one is better than the other?