Tagged Questions
1
vote
1answer
16 views
OpenCV TypeError: contour is not a numpy array, neither a scalar
I'm trying to use OpenCV to extract tags from Nike images. This is a tutorial code taken from:
http://opencv-code.com/tutorials/ocr-ing-nikes-new-rsvp-program/
I've modified few lines of code though ...
6
votes
2answers
31 views
perform varimax rotation in python using numpy
I am working on principal component analysis of a matrix. I have already found the component matrix shown below
A = np.array([[-0.73465832 -0.24819766 -0.32045055]
[-0.3728976 ...
2
votes
1answer
30 views
Exclude enpoints in uniform mesh
I would like to create a uniform 1D mesh with N points over an interval of reals (0, pi). Currently I have the following working code:
import numpy as np
u = np.linspace(0, np.pi, N+1, endpoint = ...
5
votes
2answers
75 views
Non-trivial sums of outer products without temporaries in numpy
The actual problem I wish to solve is, given a set of N unit vectors and another set of M vectors calculate for each of the unit vectors the average of the absolute value of the dot product of it with ...
3
votes
1answer
36 views
NaNs in pandas.DataFrame not printing to Excel
I have a pandas.DataFrame which contains numpy.nan floats. When using the Excel writer however, the fields where there should be numpy.nan floats are blank. I would expected at least a string ...
3
votes
3answers
83 views
Python Sigma Sums
I have a list of values
x=[1,-1,-1,1,1,-1,1,-1,1,-1]
and I have another blank list
y=[ ]
I am trying to create a function that will take a sigma sum of values in x and store them in y.
For ...
0
votes
2answers
28 views
numpy's loadtxt gives error converting to int when string contains decimal
I'm having trouble trying to load a txt file into a structured array.
Here's a simple example showing the problem.
This works fine:
import numpy as np
from StringIO import StringIO
in1 = ...
0
votes
2answers
41 views
Find all the missing directed edges in an adjacency matrix
I use a numpy matrix to represent a directed graph, like this:
0 0 0
1 0 1
1 0 0
Given such a matrix, I want to find all the missing directed edges for which there exists a directed edge in ...
4
votes
1answer
34 views
Read a 3d Array from File
Lets say I have a file with the following values:
1 2
3 4
11 12
13 14
and I want to read them as a numpy 2x2x2 array. The standard command np.loadtxt('testfile') reads them in as lots of vectors ...
2
votes
1answer
42 views
Taking up too much memory - python
I wrote a recursive function that exhaustively generates matrices of certain characteristics.
The function is as such:
def heavies(rowSums,colSums,colIndex,matH):
if colIndex == len(colSums) - 1:
...
1
vote
1answer
33 views
Polynomial fitting problems in numpy
I was trying to implement a standard polynomial fitting program, and came across a problem that I could not understand. Here is the code where I have a sample x and y data, which I fit using the ...
1
vote
0answers
56 views
Generate any random number from a CDF in python
I have a piece of python code that is suppose to generate a random number from a CDF distribution, but the random numbers it produces are only 8 different values. I am wanting any value with in the ...
2
votes
1answer
56 views
Can numpy einsum() perform outer addition?
In numpy, we can perform "outer addition" between two vectors a and b like this:
a=np.c_[1,2,3]
b=np.c_[4,5,6]
result=a+b.T # alternatively this can be a.T+b
Is it possible to use einsum to make ...
3
votes
2answers
41 views
numpy.nan weird behaviour in hashed object
I am experiencing a weird behaviour when using numpy.nan that I can't understand.
Here is a minimal example:
from numpy import nan
def _bool3key(x):
"""
Defines the keys used to order the list.
...
2
votes
1answer
34 views
Reduce Two Pandas Series to a Single One
Problem:
I'd like to take Series 1 and Series 2 and create a new Series with values (series 1, Series 2). Essentially, I have two pandas series that I would like to combine into one. Although the ...
1
vote
1answer
19 views
Using df.apply() with a Pandas MuliIndex / carrying out operations on hierarchical index rows?
Question
What is an efficient way to carry out numerical operations to hierarchical index rows?
Problem
I have a large dataframe, over 1gb, that is indexed by year and then by country code. A ...
3
votes
1answer
53 views
Gaussian Smoothing an image in python
I am very new to programming in python, and im still trying to figure everything out, but I have a problem trying to gaussian smooth or convolve an image. This is probably an easy fix, but I've spent ...
1
vote
0answers
67 views
Python float types vs Decimal
I am an intern at TCD, Physics.
I wrote a code to perform some data analysis on random particle packings. The code is written in Python.
The code reads in columns of data from a .txt file, provided ...
2
votes
1answer
42 views
Modify numpy array column by column inside a loop
Is there a way to modify a numpy array inside a loop column by column?
I expect this could be done by some code like that:
import numpy as n
cnA=n.array([[10,20]]).T
mnX=n.array([[1,2],[3,4]])
for ...
0
votes
1answer
28 views
Matplotlib fill blank image line by line, when I receive data from socket
I have data coming from a socket.
I want in the beginning to create an empty image, then update this image every time I receive the data from the socket.
The problem is when I receive a huge amount of ...
3
votes
1answer
50 views
Please clarify the following Python numpy array initialization and splicing examples
I am using
Python version 2.6
and learning numpy version 1.3.
I have tried out several numpy array initialization and column splicing examples below, and added some inline questions as comments and a ...
1
vote
1answer
55 views
Kurtosis,Skewness of a bar graph? - Python
What is an efficient method for determining the skew/kurtosis of a bar graph in python? Considering that bar graphs are not binned (unlike histograms) this question would not make a lot of sense but ...
0
votes
1answer
22 views
Port Python virtualenv to another system
I am using many python packages like numpy, bottleneck, h5py, ... for my daily work on my computer. Since I am root on this machine it is no problem to install these packages. However I would like to ...
2
votes
2answers
47 views
Vectorizing operation in NumPy
Is there a general way to vectorize these kind of operations in NumPy?
In [2]: N = 8
In [3]: ll = np.arange(8)
In [4]: arr = np.zeros(ll.shape + (2, 2))
In [5]: ll.shape
Out[5]: (8,)
In [6]: ...
1
vote
1answer
17 views
apply fromiter over matrix
Why does fromiter fail if I want to apply a function over the entire matrix?
>>> aaa = np.matrix([[2],[23]])
>>> np.fromiter( [x/2 for x in aaa], np.float)
array([ 1., 11.])
...
2
votes
2answers
94 views
Improving Numpy speed for Gauss-Seidel (Jacobi) Solver
This question is a follow-up to a recent question posted regarding MATLAB being twice as fast as Numpy.
I currently have a Gauss-Seidel solver implemented in both MATLAB and Numpy which acts on a 2D ...
2
votes
2answers
37 views
Expanding NumPy array over extra dimension
What is the easiest way to expand a given NumPy array over an extra dimension?
For example, suppose I have
>>> np.arange(4)
array([0, 1, 2, 3])
>>> _.shape
(4,)
>>> ...
2
votes
2answers
31 views
Numpy randint appending
So im generating a random list with numpy named heights...
heights = random.randint(10, size=random.randint(20))
Im using this list for testing purposes, but I have one condition, I need to append ...
1
vote
1answer
41 views
Pass percentiles to pandas agg function
I want to pass the numpy percentile() function through pandas' agg() function as I do below with various other numpy statistics functions.
Right now I have a dataframe that looks like this:
...
2
votes
2answers
43 views
Numpy, python: automatically expand dimensions of arrays when broadcasting
Consider the following exercise in Numpy array broadcasting.
import numpy as np
v = np.array([[1.0, 2.0]]).T # column array
A2 = np.random.randn(2,10) # 2D array
A3 = np.random.randn(2,10,10) # 3D
...
