[Numpy-discussion] initializing an array of lists
I want to build a 2D array of lists, and so I need to initialize the array with empty lists : myarray = array([[[],[],[]] ,[[],[],[]]]) Is there a clever way to do this? I could define the array myarray = zeros( (xdim,ydim), dtype=object) and then iterate through the elements initializing then to empty lists, but surely there is a better way. -- --- | Alan K. Jackson| To see a World in a Grain of Sand | | a...@ajackson.org | And a Heaven in a Wild Flower, | | www.ajackson.org | Hold Infinity in the palm of your hand | | Houston, Texas | And Eternity in an hour. - Blake | --- ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] initializing an array of lists
On 11/7/2009 10:56 PM, a...@ajackson.org wrote: > I want to build a 2D array of lists, and so I need to initialize the > array with empty lists : > > myarray = array([[[],[],[]] ,[[],[],[]]]) [[[] for i in range(3)] for j in range(2) ] fwiw, Alan Isaac ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] initializing an array of lists
>On 11/7/2009 10:56 PM, a...@ajackson.org wrote: >> I want to build a 2D array of lists, and so I need to initialize the >> array with empty lists : >> >> myarray = array([[[],[],[]] ,[[],[],[]]]) > > >[[[] for i in range(3)] for j in range(2) ] > >fwiw, >Alan Isaac Thanks! I like that - concise and a little strange. 8-) -- --- | Alan K. Jackson| To see a World in a Grain of Sand | | a...@ajackson.org | And a Heaven in a Wild Flower, | | www.ajackson.org | Hold Infinity in the palm of your hand | | Houston, Texas | And Eternity in an hour. - Blake | --- ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] initializing an array of lists
On Saturday 07 November 2009 22:56:29 a...@ajackson.org wrote: > I want to build a 2D array of lists, and so I need to initialize the > array with empty lists : > > myarray = array([[[],[],[]] ,[[],[],[]]]) In [1]: [[[]]*3]*2 Out[1]: [[[], [], []], [[], [], []]] Hope this helps. Ravi ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] initializing an array of lists
On Sun, Nov 8, 2009 at 5:02 PM, Ravi wrote: > On Saturday 07 November 2009 22:56:29 a...@ajackson.org wrote: >> I want to build a 2D array of lists, and so I need to initialize the >> array with empty lists : >> >> myarray = array([[[],[],[]] ,[[],[],[]]]) > > > In [1]: [[[]]*3]*2 > Out[1]: [[[], [], []], [[], [], []]] Have to be careful with that one: >> x = [[[]]*3]*2 >> x[0][0] = [] >> x [[[], [], []], [[], [], []]] but not with this one: >> x = [[[] for i in range(3)] for j in range(2)] >> x[0][0] = [] >> x [[[], [], []], [[], [], []]] ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] initializing an array of lists
a...@ajackson.org wrote: > myarray = zeros( (xdim,ydim), dtype=object) > and then iterate through the elements initializing then to empty lists, but > surely there is a better way. I tried this: In [3]: a = np.empty((2,3), dtype=np.object) In [5]: a[:,:] = [] but got: ValueError: shape mismatch: objects cannot be broadcast to a single shape Is that a bug? Or is it simply too ambiguous for numpy to figure out what the heck I want? -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R(206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] initializing an array of lists
On Mon, Nov 9, 2009 at 12:00, Christopher Barker wrote: > a...@ajackson.org wrote: >> myarray = zeros( (xdim,ydim), dtype=object) >> and then iterate through the elements initializing then to empty lists, but >> surely there is a better way. > > I tried this: > > In [3]: a = np.empty((2,3), dtype=np.object) > > In [5]: a[:,:] = [] > > but got: > > ValueError: shape mismatch: objects cannot be broadcast to a single shape > > Is that a bug? Or is it simply too ambiguous for numpy to figure out > what the heck I want? The latter. In any case, you wouldn't want each element to be the same list object. -- 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 ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] initializing an array of lists
Sat, 07 Nov 2009 21:56:29 -0600, alan wrote: > I want to build a 2D array of lists, and so I need to initialize the > array with empty lists : > > myarray = array([[[],[],[]] ,[[],[],[]]]) > > Is there a clever way to do this? I could define the array > > myarray = zeros( (xdim,ydim), dtype=object) and then iterate through the > elements initializing then to empty lists, but surely there is a better > way. This question seems to come up from time to time (= maybe should be a FAQ?). You can for example vectorize the list constructor: >>> filler = np.frompyfunc(lambda x: list(), 1, 1) >>> a = np.empty((3, 4), dtype=np.object) >>> filler(a, a); array([[[], [], [], []], [[], [], [], []], [[], [], [], []]], dtype=object) >>> a[0,3].append(9) >>> a array([[[], [], [], [9]], [[], [], [], []], [[], [], [], []]], dtype=object) -- Pauli Virtanen ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
