Suppose you have a matrix M whose (i,j)-th element equals M_ij = 2*i + 3*j One way to define this matrix would be i, j = np.indices((2,3)) M = 2*i + 3*j which yields array([[0, 3, 6], [2, 5, 8]]) In other words, np.indices returns arrays which can be used as indices. The elements in … Read more
You can achieve same result in Tensorflow using not_equal and where methods. zero = tf.constant(0, dtype=tf.float32) where = tf.not_equal(A, zero) where is a tensor of the same shape as A holding True or False, in the following case [[True, False], [False, True]] This would be sufficient to select zero or non-zero elements from A. If … Read more
>>> [i for i,v in enumerate(a) if v > 4] [4, 5, 6, 7, 8] enumerate returns the index and value of each item in an array. So if the value v is greater than 4, include the index i in the new array. Or you can just modify your list in place and exclude … Read more
RHS first and then LHS. And at any side, the evaluation order is left to right. a[-1] += a.pop() is same as, a[-1] = a[-1] + a.pop() a = [1,2,3] a[-1] = a[-1] + a.pop() # a = [1, 6] See how the behavior changes when we change the order of the operations at RHS, … Read more
s=”long string that I want to split up” indices = [0,5,12,17] parts = [s[i:j] for i,j in zip(indices, indices[1:]+[None])] returns [‘long ‘, ‘string ‘, ‘that ‘, ‘I want to split up’] which you can print using: print ‘\n’.join(parts) Another possibility (without copying indices) would be: s=”long string that I want to split up” indices = … Read more
“Indices” is the mathematical formulation whereas in publishing they use “indexes” (which is probably why so many people in IT consider “indices” to be more correct than “indexes”). I think that a table index is analogous to an index in a book rather than an exponent in maths, so the publishing variant is the appropriate … Read more
You can use a list of tuples, but the convention is different from what you want. numpy expects a list of row indices, followed by a list of column values. You, apparently, want to specify a list of (x,y) pairs. http://docs.scipy.org/doc/numpy/reference/arrays.indexing.html#integer-array-indexing The relevant section in the documentation is ‘integer array indexing’. Here’s an example, seeking … Read more
>>> a.argmax(axis=0) array([1, 1, 0])
Unfortunately, lapply only gives you the elements of the vector you pass it. The usual work-around is to pass it the names or indices of the vector instead of the vector itself. But note that you can always pass in extra arguments to the function, so the following works: x <- list(a=11,b=12,c=13) # Changed to … Read more