list of tuples vs tuple of lists

Hi,

I use the API of matplotlib and have a basic problem:

Up to now I am used to gather my data into a list of tuples. But
matplotlib uses serveral lists instead.

Example:
  me: [(date1, count1), (date2, count2), ...]
  matplotlib: ax.plot_date(dates, counts)

Finally I use something like this quite often:
   method([item[0] for item in items], [item[1] for item in items])
But I think thats to much looping.

That's my personal problem, but I think a more pythonic
API would be nice...

  Thomas

···

--
Thomas Guettler, http://www.thomas-guettler.de/
E-Mail: guettli (*) thomas-guettler + de

You could use the (admittedly inscrutable) "unzip" technique:

ax.plot_date(*zip(*items))

See this blog post for explanation:

http://paddy3118.blogspot.com/2007/02/unzip-un-needed-in-python.html

If you use Numpy arrays, of course, you could use slicing, which, IMHO, is clearer:

items = numpy.asarray(items)
ax.plot_date(items[:,0], items[:,1])

Mike

Thomas Guettler wrote:

···

Hi,

I use the API of matplotlib and have a basic problem:

Up to now I am used to gather my data into a list of tuples. But
matplotlib uses serveral lists instead.

Example:
  me: [(date1, count1), (date2, count2), ...]
  matplotlib: ax.plot_date(dates, counts)

Finally I use something like this quite often:
   method([item[0] for item in items], [item[1] for item in items])
But I think thats to much looping.

That's my personal problem, but I think a more pythonic
API would be nice...

  Thomas

--
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA

You could use the (admittedly inscrutable) "unzip" technique:

ax.plot_date(*zip(*items))

See this blog post for explanation:

http://paddy3118.blogspot.com/2007/02/unzip-un-needed-in-python.html

If you use Numpy arrays, of course, you could use slicing, which, IMHO,
is clearer:

items = numpy.asarray(items)
ax.plot_date(items[:,0], items[:,1])

if items is a numpy array you can even do:

···

On Thu, Oct 23, 2008 at 6:35 AM, Michael Droettboom <mdroe@...86...> wrote:

pylab.plot(*items.T)

Mike

Thomas Guettler wrote:

Hi,

I use the API of matplotlib and have a basic problem:

Up to now I am used to gather my data into a list of tuples. But
matplotlib uses serveral lists instead.

Example:
  me: [(date1, count1), (date2, count2), ...]
  matplotlib: ax.plot_date(dates, counts)

Finally I use something like this quite often:
   method([item[0] for item in items], [item[1] for item in items])
But I think thats to much looping.

That's my personal problem, but I think a more pythonic
API would be nice...

  Thomas

--
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA

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