In Python, I have an ndarray y that is printed as array([0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1]) I’m trying to count how many 0s and how many 1s are there in this array. But when I type y.count(0) or y.count(1), it says numpy.ndarray object has no attribute count What … Read more
What is the most efficient way to map a function over a numpy array? The way I’ve been doing it in my current project is as follows: import numpy as np x = np.array([1, 2, 3, 4, 5]) # Obtain array of square of each element in x squarer = lambda t: t ** 2 … Read more
I know there is a method for a Python list to return the first index of something: >>> l = [1, 2, 3] >>> l.index(2) 1 Is there something like that for NumPy arrays? 18 s 18 Yes, given an array, array, and a value, item to search for, you can use np.where as: itemindex … Read more
Suppose I have: test = numpy.array([[1, 2], [3, 4], [5, 6]]) test[i] gets me ith line of the array (eg [1, 2]). How can I access the ith column? (eg [1, 3, 5]). Also, would this be an expensive operation? 8 s 8 >>> test[:,0] array([1, 3, 5]) Similarly, >>> test[1,:] array([3, 4]) lets you … Read more
A numpy matrix can be reshaped into a vector using reshape function with parameter -1. But I don’t know what -1 means here. For example: a = numpy.matrix([[1, 2, 3, 4], [5, 6, 7, 8]]) b = numpy.reshape(a, -1) The result of b is: matrix([[1, 2, 3, 4, 5, 6, 7, 8]]) Does anyone know … Read more
I am interested in knowing how to convert a pandas dataframe into a NumPy array. dataframe: import numpy as np import pandas as pd index = [1, 2, 3, 4, 5, 6, 7] a = [np.nan, np.nan, np.nan, 0.1, 0.1, 0.1, 0.1] b = [0.2, np.nan, 0.2, 0.2, 0.2, np.nan, np.nan] c = [np.nan, 0.5, … Read more
NumPy proposes a way to get the index of the maximum value of an array via np.argmax. I would like a similar thing, but returning the indexes of the N maximum values. For instance, if I have an array, [1, 3, 2, 4, 5], function(array, n=3) would return the indices [4, 3, 1] which correspond … Read more
Is there a way to dump a NumPy array into a CSV file? I have a 2D NumPy array and need to dump it in human-readable format. 1Best Answer 11 numpy.savetxt saves an array to a text file. import numpy a = numpy.asarray([ [1,2,3], [4,5,6], [7,8,9] ]) numpy.savetxt(“foo.csv”, a, delimiter=”,”)
I have two points in 3D: (xa, ya, za) (xb, yb, zb) And I want to calculate the distance: dist = sqrt((xa-xb)^2 + (ya-yb)^2 + (za-zb)^2) What’s the best way to do this with NumPy, or with Python in general? I have: import numpy a = numpy.array((xa ,ya, za)) b = numpy.array((xb, yb, zb)) 23 … Read more
When I print a numpy array, I get a truncated representation, but I want the full array. Is there any way to do this? Examples: >>> numpy.arange(10000) array([ 0, 1, 2, …, 9997, 9998, 9999]) >>> numpy.arange(10000).reshape(250,40) array([[ 0, 1, 2, …, 37, 38, 39], [ 40, 41, 42, …, 77, 78, 79], [ 80, … Read more
