Hello, 'len' is a (pretty basic) python builtin function for getting the length of anything with a list-like interface. (Or more generally, getting the size of anything that is sized, e.g. a set or dictionary.)
Numpy arrays offer a list-like interface allowing you to iterate along their first dimension, etc. (*) Thus, len(numpy_array) is equivalent to numpy_array.shape[0], which is the number of elements along the first dimension of the array. Zach (*) For example, this is useful if you've got numerous data vectors packed into an array along the first dimension, and want to iterate across the different vectors. a = numpy.ones((number_of_data_elements, size_of_data_element)) for element in a: # element is a 1-D array with a length of 'size_of_data_element' Note further that this works even if your data elements are multi- dimensional; i.e. the above works the same if: element_shape = (x,y,z) a = numpy.ones((number_of_data_elements,)+element_shape) for element in a: # element is a 3-D array with a shape of (x,y,z) On Sep 5, 2007, at 2:40 PM, Robert Dailey wrote: > Thanks for your response. > > I was not able to find len() in the numpy documentation at the > following link: > http://www.scipy.org/doc/numpy_api_docs/namespace_index.html > > Perhaps I'm looking in the wrong location? > > On 9/5/07, Matthieu Brucher <[EMAIL PROTECTED] > wrote: > > 2007/9/5, Robert Dailey < [EMAIL PROTECTED]>: Hi, > > I have two questions: > > 1) Is there any way in numpy to represent vectors? Currently I'm > using 'array' for vectors. > > > A vector is an array with one dimension, it's OK. You could use a > matrix of dimension 1xn or nx1 as well. > > > 2) Is there a way to calculate the magnitude (length) of a vector > in numpy? > > Yes, len(a) > > Matthieu > > _______________________________________________ > Numpy-discussion mailing list > Numpy-discussion@scipy.org > http://projects.scipy.org/mailman/listinfo/numpy-discussion > > > _______________________________________________ > Numpy-discussion mailing list > Numpy-discussion@scipy.org > http://projects.scipy.org/mailman/listinfo/numpy-discussion _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion