Numpy – add row to array
What is X? If it is a 2D-array, how can you then compare its row to a number: i < 3? EDIT after OP’s comment: add to A all rows from X where the first element < 3:
numpy
Create numpy matrix filled with NaNs
You rarely need loops for vector operations in numpy. You can create an uninitialized array and assign to all entries at once: I have timed the alternatives a[:] = numpy.nan here and a.fill(numpy.nan) as posted by Blaenk: The timings show a preference for ndarray.fill(..) as the faster alternative. OTOH, I like numpy’s convenience implementation where you can assign values to whole … Read more
Compute a confidence interval from sample data
you can calculate like this way.
What are the differences between numpy arrays and matrices? Which one should I use?
Numpy matrices are strictly 2-dimensional, while numpy arrays (ndarrays) are N-dimensional. Matrix objects are a subclass of ndarray, so they inherit all the attributes and methods of ndarrays. The main advantage of numpy matrices is that they provide a convenient notation for matrix multiplication: if a and b are matrices, then a*b is their matrix product. On the other hand, as … Read more
Root mean square of a function in python
I’m going to assume that you want to compute the expression given by the following pseudocode: i.e. the square root of the mean of the squared values of elements of y. In numpy, you can simply square y, take its mean and then its square root as follows: So, for example: Do clarify your question … Read more
Coalesce values from 2 columns into a single column in a pandas dataframe
use combine_first():
How to add a new row to an empty numpy array
The way to “start” the array that you want is: Which is an empty array but it has the proper dimensionality. Then be sure to append along axis 0: But, @jonrsharpe is right. In fact, if you’re going to be appending in a loop, it would be much faster to append to a list as … Read more
ImportError in importing from sklearn: cannot import name check_build
Worked for me after installing scipy.
IndexError: index 2 is out of bounds for axis 0 with size 2
(Answer courtsey of Warren Weckesser, provided in the comments to the question.) You have Y0 = [E0, C0]. If the system is three-dimensional, then Y0 must have three values, so something like Y0 = [E0, C0, l0] where l0 is the initial condition for l(t).
Python 3: Multiply a vector by a matrix without NumPy
The Numpythonic approach: (using numpy.dot in order to get the dot product of two matrices) The Pythonic approach: The length of your second for loop is len(v) and you attempt to indexing v based on that so you got index Error . As a more pythonic way you can use zip function to get the columns of a list then use starmap and mul within a list comprehension: