Re: [Numpy-discussion] Slices from an index list
On Wed, Apr 11, 2012 at 4:28 AM, Mads Ipsen madsip...@gmail.com wrote: Hi, Suppose a have an array of indices, say indices = [0,1,2,3,5,7,8,9,10,12,13,14] Then the following slices a = slice(0,4) b = slice(4,5) c = slice(5,9) d = slice(9,12) provide information about all the consecutive parts of the index list. Given the list of indices, is there some nifty numpy function that can generate the above slices for me (or their start and stop values)? Here's one way you could do it: In [43]: indices = [0,1,2,3,5,7,8,9,10,12,13,14] In [44]: jumps = where(diff(indices) != 1)[0] + 1 In [45]: starts = hstack((0, jumps)) In [46]: ends = hstack((jumps, len(indices))) In [47]: slices = [slice(start, end) for start, end in zip(starts, ends)] In [48]: slices Out[48]: [slice(0, 4, None), slice(4, 5, None), slice(5, 9, None), slice(9, 12, None)] Warren ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Slices from an index list
Here's one way you could do it: In [43]: indices = [0,1,2,3,5,7,8,9,10,12,13,14] In [44]: jumps = where(diff(indices) != 1)[0] + 1 In [45]: starts = hstack((0, jumps)) In [46]: ends = hstack((jumps, len(indices))) In [47]: slices = [slice(start, end) for start, end in zip(starts, ends)] In [48]: slices Out[48]: [slice(0, 4, None), slice(4, 5, None), slice(5, 9, None), slice(9, 12, None)] If you're only going to use the slices to divide up the list, you could use numpy.split and skip creating the slice objects: indices = [0,1,2,3,5,7,8,9,10,12,13,14] jumps = numpy.where(numpy.diff(indices) != 1)[0] + 1 numpy.split(indices, jumps) giving: [array([0, 1, 2, 3]), array([5]), array([ 7, 8, 9, 10]), array([12, 13, 14])] Zach (btw, Warren, the method to calculate the jumps is cute. I'll have to remember that.) ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Slices from an index list
On 11/04/2012 13:42, Warren Weckesser wrote: On Wed, Apr 11, 2012 at 4:28 AM, Mads Ipsen madsip...@gmail.com mailto:madsip...@gmail.com wrote: Hi, Suppose a have an array of indices, say indices = [0,1,2,3,5,7,8,9,10,12,13,14] Then the following slices a = slice(0,4) b = slice(4,5) c = slice(5,9) d = slice(9,12) provide information about all the consecutive parts of the index list. Given the list of indices, is there some nifty numpy function that can generate the above slices for me (or their start and stop values)? Here's one way you could do it: In [43]: indices = [0,1,2,3,5,7,8,9,10,12,13,14] In [44]: jumps = where(diff(indices) != 1)[0] + 1 In [45]: starts = hstack((0, jumps)) In [46]: ends = hstack((jumps, len(indices))) In [47]: slices = [slice(start, end) for start, end in zip(starts, ends)] In [48]: slices Out[48]: [slice(0, 4, None), slice(4, 5, None), slice(5, 9, None), slice(9, 12, None)] Warren ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion Thanks - very helpful! -- +-+ | Mads Ipsen | +--+--+ | Gåsebæksvej 7, 4. tv | | | DK-2500 Valby| phone: +45-29716388 | | Denmark | email: mads.ip...@gmail.com | +--+--+ ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Slices from an index list
On 11/04/2012 14:19, Zachary Pincus wrote: Here's one way you could do it: In [43]: indices = [0,1,2,3,5,7,8,9,10,12,13,14] In [44]: jumps = where(diff(indices) != 1)[0] + 1 In [45]: starts = hstack((0, jumps)) In [46]: ends = hstack((jumps, len(indices))) In [47]: slices = [slice(start, end) for start, end in zip(starts, ends)] In [48]: slices Out[48]: [slice(0, 4, None), slice(4, 5, None), slice(5, 9, None), slice(9, 12, None)] If you're only going to use the slices to divide up the list, you could use numpy.split and skip creating the slice objects: indices = [0,1,2,3,5,7,8,9,10,12,13,14] jumps = numpy.where(numpy.diff(indices) != 1)[0] + 1 numpy.split(indices, jumps) giving: [array([0, 1, 2, 3]), array([5]), array([ 7, 8, 9, 10]), array([12, 13, 14])] Zach (btw, Warren, the method to calculate the jumps is cute. I'll have to remember that.) ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion Thanks - very helpful! -- +-+ | Mads Ipsen | +--+--+ | Gåsebæksvej 7, 4. tv | | | DK-2500 Valby| phone: +45-29716388 | | Denmark | email: mads.ip...@gmail.com | +--+--+ ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
