How does one add rows to a numpy array? I have an array A: A = array([[0, 1, 2], [0, 2, 0]]) I wish to add rows to this array from another array X if the first element of each row in X meets a specific condition. Numpy arrays do not have a method ‘append’ … Read more
Using Matplotlib, I want to plot a 2D heat map. My data is an n-by-n Numpy array, each with a value between 0 and 1. So for the (i, j) element of this array, I want to plot a square at the (i, j) coordinate in my heat map, whose color is proportional to the … Read more
This question already has answers here: Closed 9 years ago. Possible Duplicate: A Transpose/Unzip Function in Python I’ve used the zip() function from the numpy library to sort tuples and now I have a list containing all the tuples. I had since modified that list and now I would like to restore the tuples so … Read more
Using standard Python arrays, I can do the following: arr = [] arr.append([1,2,3]) arr.append([4,5,6]) # arr is now [[1,2,3],[4,5,6]] However, I cannot do the same thing in numpy. For example: arr = np.array([]) arr = np.append(arr, np.array([1,2,3])) arr = np.append(arr, np.array([4,5,6])) # arr is now [1,2,3,4,5,6] I also looked into vstack, but when I use … Read more
In keeping with the “There’s only one obvious way to do it”, how do you get the magnitude of a vector (1D array) in Numpy? def mag(x): return math.sqrt(sum(i**2 for i in x)) The above works, but I cannot believe that I must specify such a trivial and core function myself. 8 Answers 8
I am looking for a function that takes as input two lists, and returns the Pearson correlation, and the significance of the correlation. 17 Answers 17
I have to make a Lagrange polynomial in Python for a project I’m doing. I’m doing a barycentric style one to avoid using an explicit for-loop as opposed to a Newton’s divided difference style one. The problem I have is that I need to catch a division by zero, but Python (or maybe numpy) just … Read more
I am trying to write a Pandas dataframe (or can use a numpy array) to a mysql database using MysqlDB . MysqlDB doesn’t seem understand ‘nan’ and my database throws out an error saying nan is not in the field list. I need to find a way to convert the ‘nan’ into a NoneType. Any … Read more
I have a pandas dataframe and I wish to divide it to 3 separate sets. I know that using train_test_split from sklearn.cross_validation, one can divide the data in two sets (train and test). However, I couldn’t find any solution about splitting the data into three sets. Preferably, I’d like to have the indices of the … Read more
Consider the following code: avgDists = np.array([1, 8, 6, 9, 4]) ids = avgDists.argsort()[:n] This gives me indices of the n smallest elements. Is it possible to use this same argsort in descending order to get the indices of n highest elements? 9 Answers 9
