Re: unpacking vars from list of tuples

2009-09-17 Thread Chris Colbert 
if you have numpy installed:


ln[12]: import numpy as np
In [13]: k = np.array([('a', 'bob', 'c'), ('p', 'joe', 'd'), ('x',
'mary', 'z')])

In [14]: k
Out[14]:
array([['a', 'bob', 'c'],
   ['p', 'joe', 'd'],
   ['x', 'mary', 'z']],
  dtype='|S4')

In [15]: k[:,1]
Out[15]:
array(['bob', 'joe', 'mary'],
  dtype='|S4')
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Re: unpacking vars from list of tuples

2009-09-17 Thread Ross 


Cool - Now that would be some seriously dense, efficient code!   Will  
have to play with numpy sometime.



R.


On 17-Sep-09, at 12:25 PM, Chris Colbert wrote:


if you have numpy installed:


ln[12]: import numpy as np
In [13]: k = np.array([('a', 'bob', 'c'), ('p', 'joe', 'd'), ('x',
'mary', 'z')])

In [14]: k
Out[14]:
array([['a', 'bob', 'c'],
   ['p', 'joe', 'd'],
   ['x', 'mary', 'z']],
  dtype='|S4')

In [15]: k[:,1]
Out[15]:
array(['bob', 'joe', 'mary'],
  dtype='|S4')


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unpacking vars from list of tuples

2009-09-15 Thread Ross 
I'm inexperienced with some of the fancy list slicing syntaxes where
python shines.

If I have a list of tuples:

   k=[(a, bob, c), (p, joe, d), (x, mary, z)]

and I want to pull the middle element out of each tuple to make a new
list:

myList = [bob, joe, mary]

is there some compact way to do that?  I can imagine the obvious one
of

myList = []
for a in k:
   myList.append(a[1])

But I'm guessing Python has something that will do that in one line...

Any suggestion is appreciated...

Ross.
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Re: unpacking vars from list of tuples

2009-09-15 Thread Chris Rebert 
On Tue, Sep 15, 2009 at 2:51 PM, Ross ros...@gmail.com wrote:
 I'm inexperienced with some of the fancy list slicing syntaxes where
 python shines.

 If I have a list of tuples:

   k=[(a, bob, c), (p, joe, d), (x, mary, z)]

 and I want to pull the middle element out of each tuple to make a new
 list:

 myList = [bob, joe, mary]

 is there some compact way to do that?  I can imagine the obvious one
 of

 myList = []
 for a in k:
   myList.append(a[1])

 But I'm guessing Python has something that will do that in one line...

Indeed:

myList = [a[1] for a in k]

Google for list comprehension python.

Cheers,
Chris
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Re: unpacking vars from list of tuples

2009-09-15 Thread Andre Engels 
On Tue, Sep 15, 2009 at 11:51 PM, Ross ros...@gmail.com wrote:
 I'm inexperienced with some of the fancy list slicing syntaxes where
 python shines.

 If I have a list of tuples:

   k=[(a, bob, c), (p, joe, d), (x, mary, z)]

 and I want to pull the middle element out of each tuple to make a new
 list:

 myList = [bob, joe, mary]

 is there some compact way to do that?  I can imagine the obvious one
 of

 myList = []
 for a in k:
   myList.append(a[1])

 But I'm guessing Python has something that will do that in one line...

 Any suggestion is appreciated...

You can use a list comprehension:

myList = [a[1] for a in k]




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Re: unpacking vars from list of tuples

2009-09-15 Thread Wolfram Hinderer 
On 15 Sep., 23:51, Ross ros...@gmail.com wrote:

 If I have a list of tuples:

    k=[(a, bob, c), (p, joe, d), (x, mary, z)]

 and I want to pull the middle element out of each tuple to make a new
 list:

 myList = [bob, joe, mary]

if a tuple is OK: zip(*k)[1]
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Re: unpacking vars from list of tuples

2009-09-15 Thread Tim Chase 

If I have a list of tuples:

   k=[(a, bob, c), (p, joe, d), (x, mary, z)]

and I want to pull the middle element out of each tuple to make a new
list:

myList = [bob, joe, mary]

is there some compact way to do that?  I can imagine the obvious one
of

myList = []
for a in k:
   myList.append(a[1])

But I'm guessing Python has something that will do that in one line...


To add some readability to the other suggested solutions, I'd use
tuple unpacking

 my_list = [name for status, name, code in k]

Not knowing what [0] and [2] are, I randomly designated them as 
status and code, but you likely have your own meanings.  If 
you don't, you can always just use the _ convention:


  my_list = [name for _, name, _ in k]
  # or
  my_list = [name for (_, name, _) in k]

As an aside, my_list is preferred over myList in common 
Python practice.  I don't know if there's a preferred convention 
for with vs without the parens in such a tuple-unpacking list 
comprehension.


-tkc







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Re: unpacking vars from list of tuples

2009-09-15 Thread Ross 
On Sep 15, 6:00 pm, Andre Engels andreeng...@gmail.com wrote:
 On Tue, Sep 15, 2009 at 11:51 PM, Ross ros...@gmail.com wrote:
  I'm inexperienced with some of the fancy list slicing syntaxes where
  python shines.

  If I have a list of tuples:

    k=[(a, bob, c), (p, joe, d), (x, mary, z)]

  and I want to pull the middle element out of each tuple to make a new
  list:

  myList = [bob, joe, mary]

  is there some compact way to do that?  I can imagine the obvious one
  of

  myList = []
Thanks both Chris and André. That's quite obvious once it's pointed
out for me.  Thanks especially for the terminology that will make
learning the related concepts a bit easier.

Ross


  for a in k:
    myList.append(a[1])

  But I'm guessing Python has something that will do that in one line...

  Any suggestion is appreciated...

 You can use a list comprehension:

 myList = [a[1] for a in k]

 --
 André Engels, andreeng...@gmail.com

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Re: unpacking vars from list of tuples

2009-09-15 Thread Ross 

Thanks Tim,

That's actually the stuff I was trying to remember.

   my_list = [name for _, name, _ in k]

I recalled using some underscores for nice dense unnamed variable  
unpacking before, but couldn't recall the process.


Thanks for that.

Ross.


On 15-Sep-09, at 6:33 PM, Tim Chase wrote:


If I have a list of tuples:
   k=[(a, bob, c), (p, joe, d), (x, mary, z)]
and I want to pull the middle element out of each tuple to make a new
list:
myList = [bob, joe, mary]
is there some compact way to do that?  I can imagine the obvious one
of
myList = []
for a in k:
   myList.append(a[1])
But I'm guessing Python has something that will do that in one  
line...


To add some readability to the other suggested solutions, I'd use
tuple unpacking

 my_list = [name for status, name, code in k]

Not knowing what [0] and [2] are, I randomly designated them as  
status and code, but you likely have your own meanings.  If you  
don't, you can always just use the _ convention:


  my_list = [name for _, name, _ in k]
  # or
  my_list = [name for (_, name, _) in k]

As an aside, my_list is preferred over myList in common Python  
practice.  I don't know if there's a preferred convention for with  
vs without the parens in such a tuple-unpacking list comprehension.


-tkc









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