Tagged Questions
0
votes
0answers
3 views
How can I apply a matrix transform to each row of a NumPy array efficiently?
Let's say I have a 2d NumPy ndarray, like so:
[[ 0, 1, 2, 3 ],
[ 4, 5, 6, 7 ],
[ 8, 9, 10, 11 ]]
Conceptually speaking, what I want to do is this:
For each row:
Transpose the row
...
2
votes
1answer
29 views
Numpy array, fill empty values for a single column
I have an array in numpy, which was generated using np.array() from a python list so my entries are strings, but some of the values are blank. Here is an example array:
['1', '1', '1', '1']
['1', ...
1
vote
0answers
7 views
Compiling a FORTRAN Module using f2py
I used to compile a FORTRAN program with f2py long time ago. But when I failed to re-compile it today. I guess the reason is not pointing to the right compiler. Last time, my machine was clean only ...
3
votes
2answers
26 views
Determine widening conversion of NumPy types
I have a library based on NumPy with a few classes that overload the arithmetic operations. The internals are a little hairy due to a significant amount of error checking, but I've run across a ...
1
vote
1answer
29 views
Could not locate executable f95, f77, xlf, ifc, g77
I'm trying to install glmnet using these instructions. When I run python setup.py and I choose the interactive option to build, I get the following Could not locate executable XXX errors. I've ...
2
votes
0answers
22 views
Numpy, Virtualenv and the “Cannot find vcvarsall.bat” issue on Windows
I'm trying to install Numpy and other packages into a virtualenv.
When I try to install it, I get an error, "cannot find vcvarsall.bat". On my main (system wide) Python, I solved this by ...
4
votes
0answers
52 views
dgemm segfaulting with large F-order matrices in scipy
I'm attempting to compute A*A.T in Python using SciPy's dgemm, but getting a segfault when A has large row dimension (~50,000) and I pass the matrices in in F-order. Of course, the resulting matrix is ...
2
votes
1answer
34 views
product of arrays of different sizes in numpy
I have two arrays, x = np.arange(3) = [0,1,2,3] and y = np.arange(4) = [0,1,2].
Is there a numpy function that gives a table of all of their products ? Or example for times this would be:
x*y = ...
0
votes
3answers
51 views
Installing NumPy with pip fails on Ubuntu
When I try:
$ sudo pip install numpy
on my Ubuntu 12.04 server, I get:
------------------------------------------------------------
/usr/local/bin/pip run on Tue Dec 10 18:25:54 2013
...
5
votes
0answers
99 views
Why is SciPy acting very differently in IPython and Python?
I wrote this test script:
import numpy as np
import scipy.linalg
n = 130
r = np.array(np.random.normal(size=(n, n)), dtype=np.float32)
e = scipy.linalg.eig(r, left=False, right=False)
print e.mean()
...
1
vote
1answer
29 views
SciPy optimize.fmin ValueError: zero-size array to reduction operation maximum which has no identity
UPDATE2: A better title (now that I understand the problem) would be:
What is the proper syntax for input in scipy optimize.fmin?
UPDATE: runnable code was requested, so the function definitions have ...
3
votes
1answer
45 views
Python scipy chisquare returns different values than R chisquare
I am trying to use scipy.stats.chisquare. I have built a toy example:
In [1]: import scipy.stats as sps
In [2]: import numpy as np
In [3]: sps.chisquare(np.array([38,27,23,17,11,4]), np.array([98, ...
1
vote
1answer
51 views
Optimal way for calculating columnwise mutual information using numpy
For a matrix of m x n, what's the optimal (fastest) way to do a Mutual Information calculation for all the columns (n x n ) ?
MI = H_of_X + H_of_Y - H_of_XY where H(X) is the Shannon Entropy of X
...
0
votes
2answers
25 views
ndim of structured arrays in numpy?
This is similarly worded question as ndim in numpy array loaded with scipy.io.loadmat? - but it's actually a lot more basic.
Say I have this structured array:
import sys
import numpy as np
from ...
0
votes
1answer
34 views
Read filenames from a textfile in python (double backslash issue)
I am trying to read a list of files from a text file. I am using the following code to do that:
filelist = input("Please Enter the filelist: ")
flist = open (os.path.normpath(filelist),"r")
fname = ...
0
votes
1answer
22 views
Keep the fitted parameters when using a cross_val_score in scikits learn
I'm trying to use scikits-learn to fit a linear model using Ridge regression. What I'd like to do is use cross validation to fit many different models, and then look at the parameter coefficients to ...
2
votes
1answer
48 views
“import matplotlib.pyplot as plt” in ipython notebook
I'm new to ipython notebook, but I have the following error message whenever I run import matplotlib.pyplot as plt. I'm using Mac. It works fine with the built-in python or Canopy. The problem only ...
-1
votes
1answer
42 views
Python something resets my random seed
My question is the exact opposite of this one.
This is an excerpt from my test file
f1 = open('seed1234','r')
f2 = open('seed7883','r')
s1 = eval(f1.read())
s2 = eval(f2.read())
f1.close()
...
0
votes
1answer
53 views
SystemError: error return without exception set
Whenever I run this code I get the above error, specifically at famList[inc]
import numpy as np
class Element:
def __init__(self,
mass,
number,
...
3
votes
1answer
45 views
How to force larger steps on scipy.optimize functions?
I have a function compare_images(k, a, b) that compares two 2d-arrays a and b
Inside the funcion, I apply a gaussian_filter with sigma=k to a My idea is to estimate how much I must to smooth image a ...
2
votes
1answer
41 views
How to import matrix from excel into numpy and then graph it?
I have a matrix in excel that I am trying to import and convert to a numpy matrix and then graph it with networkx how would I go about doing this? I do have some code but not sure if I am going about ...
0
votes
2answers
25 views
OpenCV detect if image file is colour prior to loading
I know you can use imread to get an image into a numpy array.
cv2.imread(path,0)
Loads a greyscale image and...
cv2.imread(path,1)
Loads a colour one.
I can call the second one on a greyscale ...
0
votes
2answers
25 views
How do you allow for text qualifiers using numpy genfromtext [duplicate]
I am currently trying to import some comma delimited text data into an array using the numpy library in Python. I am using the following code:
data = np.genfromtxt(fname, delimiter=',')
I get the ...
3
votes
2answers
59 views
Find index in array to which the sum of all elements is smaller than a limit, quickly
Given is a large array. I am looking for the index up to which all elements in the array add up to a number smaller than limit. I found two ways to do so:
import time as tm
import numpy as nm
# Data ...
1
vote
1answer
27 views
How do I duplicate the values for the last dimension in a numpy array?
I am getting an error in numpy when I perform the pairwise multiplication of two arrays a and b since a has dimensions 100 x 200 x 3, while b has dimensions 100 x 200. However, b contains only 0s and ...
0
votes
1answer
20 views
Trouble importing scipy.stats for scipy 0.13 build 2
I am using Enthought Canopy and recently upgraded both Scipy and numpy to the following:
scipy: 0.13 build 2
numpy: 1.8 build 1
When I attempt:
from scipy import stats
I receive the following ...
4
votes
2answers
73 views
NumPy Matrix Multiplication Efficiency for Matrix With Known Structure
I have two NxN matrices that I want to multiply together: A and B. In NumPy, I used:
import numpy as np
C = np.dot(A, B)
However, I happen to know that for matrix B only row n and column n are ...
0
votes
1answer
24 views
Convert Pandas dataframe to Sparse Numpy Matrix directly
I am creating a matrix from a Pandas dataframe as follows:
dense_matrix = numpy.array(df.as_matrix(columns = None), dtype=bool).astype(np.int)
And then into a sparse matrix with:
sparse_matrix = ...
1
vote
1answer
42 views
ValueError: The elements are 0-sized
Haven't been able to find any information on the web about this problem. I'm trying to read from a text file using numpy.
data = ...
1
vote
1answer
24 views
what is the difference between the two datasets for numpy.fft
I am trying to find the period of a sin curve and can find the right periods for sin(t).
However for sin(k*t), the frequency shifts. I do not know how it shifts.
I can adjust the value of interd below ...
0
votes
2answers
33 views
How can I plot this data?
I am trying to plot this data. I know it should be quite easy to do that but I am struggling (haven't had my coffee yet).
h = 1
m = 1
E1 = (((h**2)/(2*m)) * ((((1*np.pi)/2)+((1*np.pi)/2))**2))
E2 = ...
0
votes
2answers
42 views
Python Numpy or Pandas Linear Interpolation For Datetime related Values
I have data that looks like the following but I also have control of how it is formatted. Basically, I want to use Python with Numpy or Pandas to interpolate the dataset to achieve second by second ...
3
votes
1answer
29 views
numpy array to list formatting
How would i format a numpy array of form
data1 = np.array([[0,0,0],[0,1,1],[1,0,1],[1,1,0]])
to a list in this format:
data = [
[[0,0], [0]],
[[0,1], [1]],
[[1,0], [1]],
...
0
votes
2answers
30 views
How do you add numpy subarrays to each other?
I have used the numpy.array_split() function in order to split an array of astronomical data into a series of subarrays of known length (the number of subarrays being completely unknown and ...
1
vote
1answer
40 views
Subtracting two interleaved, differently based time-series arrays with numpy?
I have two datasets, a[ts1] and b[ts2], where ts1 and ts2 are timestamps taken at different times (in different bases?). I wanted to plot b[ts2]-a[ts1], but I think I made a mistake, in that the ...
0
votes
2answers
47 views
python, how to write conditions in a function?
How to write conditions in a function (k_over_iq)?
dt_for_all_days_np=a numpy array of numbers.
def k_over_iq(dt):
if dt !=0:
return 0.7*(1-e**(-0.01*dt**2.4))
else:
...
2
votes
1answer
44 views
Integral control system does not behave properly
Yesterday I posted a question here: ValueError and odepack.error using integrate.odeint() which I thought had been successfully answered. However I have since noticed a couple of things.
When ...
-2
votes
0answers
30 views
Python(numpy) cmputing a 2d array with a 1d array
I have the following arrays:
>>> b
array([[ 5., 4., 10., 18.],
[ 10., 1., 18., 7.],
[ 17., 2., 7., 19.]])
>>> z
array([2, 4, 6, 7])
I would like ...
0
votes
0answers
44 views
performing arithmetics with several numpy arrays [on hold]
Say I have the arrays below and perform the simple task of adding.
a = np.floor(10*random.random((3,4)))
b = np.floor(20*random.random((3,4)))
>>> a
array([[ 2., 5., 2., 2.],
...
0
votes
1answer
29 views
Wrapping C code including Python API using SWIG and distutils fails on Mac 10.8 64bits
I have been trying to wrap an existing C code into a Python module for some time now and I keep running into recurrent errors and a failed build... After an extensive look at the available ...
-1
votes
1answer
16 views
PyQt table Widget Entries to list or numpy array object
i am trying to send some data from a gui i am working on to python.
what i want to do ist write a row (gui) to a list (python) or something similar... (directly to a numpy array would be the best)...
...
0
votes
1answer
48 views
Segment Line Intersection algorithm in Numpy
I have two line segments AB: (A1,B1), (A2,B2) and axis_dx coordinate interval. I should find all points crossed by axis coordinates interval i.e.,axis_dx. I already found those points, BUT, the ...
1
vote
1answer
45 views
Build Numpy with Eigen instead of ATLAS or OpenBlas?
since Eigen looks very promising (Benchmark) I wonder if it was possible to compile numpy with the Eigen library, as it is possible to build numpy with ATLAS or with OpenBlas (or with intel-mkl). I ...
2
votes
1answer
65 views
Python: “IndexError: invalid index into a 0-size array”
Obviously, there are loads of threads concerning index errors. But I couldn't find one that helped me out.
I use numpy.loadtxt to read in a function f(a,b).
a, b, f = np.loadtxt(filename, ...
4
votes
2answers
451 views
How to obtain a gaussian filter in python
I am using python to create a gaussian filter of size 5x5.
I saw this post here where they talk about a similar thing but I didn't find the exact way to get equivalent python code to matlab function ...
2
votes
2answers
10k views
How do I find the length (or dimensions, size) of a numpy matrix in python? [duplicate]
For a numpy matrix in python
from numpy import matrix
A = matrix([[1,2],[3,4]])
How can I find the length of a row (or column) of this matrix? Equivalently, how can I know the number of rows or ...
2
votes
1answer
2k views
ValueError: object too deep for desired array
""" ___ """
from scipy.optimize import root
import numpy as np
LENGTH = 3
def process(x):
return x[0, 0] + x[0, 1] * 5
def draw(process, length):
""" """
X = ...
3
votes
4answers
2k views
How to resample a dataframe with different functions applied to each column?
I have a times series with temperature and radiation in a pandas dataframe. The time resolution is 1 minute in regular steps.
import datetime
import pandas as pd
import numpy as np
date_times = ...
83
votes
1answer
31k views
Simple Digit Recognition OCR in OpenCV-Python
I am trying to implement a "Digit Recognition OCR" in OpenCV-Python (cv2). ( It is just for learning purposes ). I would like to learn both KNearest and SVM features in OpenCV.
I have 100 ...
11
votes
2answers
7k views
plotting 3d scatter in matplotlib
I have a collection of Nx3 matrices in scipy/numpy and I'd like to make a 3 dimensional scatter of it, where the X and Y axes are determined by the values of first and second columns of the matrix, ...
