Python: find position of element in array
Have you thought about using Python list’s .index(value) method? It return the index in the list of where the first instance of the value passed in is found.
numpy
Dump a NumPy array into a csv file
numpy.savetxt saves an array to a text file.
LinAlgError: Last 2 dimensions of the array must be square
I need to solve a set of simultaneous equations of the form Ax = B for x. I’ve used the numpy.linalg.solve function, inputting A and B, but I get the error ‘LinAlgError: Last 2 dimensions of the array must be square’. How do I fix this? Here’s my code: The values of the matrix/vector are calculated earlier in … Read more
How to access the ith column of a NumPy multidimensional array?
Similarly, lets you access rows. This is covered in Section 1.4 (Indexing) of the NumPy reference. This is quick, at least in my experience. It’s certainly much quicker than accessing each element in a loop.
Purpose of `numpy.log1p( )`?
The NumPy docs give a hint: For real-valued input, log1p is accurate also for x so small that 1 + x == 1 in floating-point accuracy. So for example let’s add a tiny non-zero number and 1.0. Rounding errors make it a 1.0. If we try to take the log of that incorrect sum, we get an incorrect result (compare to WolframAlpha): But if we use log1p(), we … Read more
Calculating Covariance with Python and Numpy
When a and b are 1-dimensional sequences, numpy.cov(a,b)[0][1] is equivalent to your cov(a,b). The 2×2 array returned by np.cov(a,b) has elements equal to (where, again, cov is the function you defined above.)
ValueError: ‘object too deep for desired array’
Try this: You are trying to get the values from a whole DataFrame. That is why you get the 2D array. Each row in the array is a row of the DataFrame.
How can I use numpy.correlate to do autocorrelation?
To answer your first question, numpy.correlate(a, v, mode) is performing the convolution of a with the reverse of v and giving the results clipped by the specified mode. The definition of convolution, C(t)=∑ -∞ < i < ∞ aivt+i where -∞ < t < ∞, allows for results from -∞ to ∞, but you obviously can’t store an infinitely long array. So it has to … Read more
Cannot convert list to array: ValueError: only one element tensors can be converted to Python scalars
It seems like you have a list of tensors. For each tensor you can see its size() (no need to convert to list/numpy). If you insist, you can convert a tensor to numpy array using numpy(): Return a list of tensor shapes: Returns a list of numpy arrays: In terms of performance, it is always best to avoid … Read more
load csv into 2D matrix with numpy for plotting
Pure numpy Check out the loadtxt documentation. You can also use python’s csv module: You will have to convert it to your favorite numeric type. I guess you can write the whole thing in one line: result = numpy.array(list(csv.reader(open(“test.csv”, “rb”), delimiter=”,”))).astype(“float”) Added Hint: You could also use pandas.io.parsers.read_csv and get the associated numpy array which can be faster.