I have this code where I want to reference all elements of m in matlab:
NNanm = sum(isnan(m(:)));
How would I tell python to reference all the elements of m?
If I understand your code correctly, you count all nan elements in the matrix. If so, you can do the equivalent thing in python this using numpy with the following code:
import numpy as np
np.count_nonzero(np.isnan(m))
If you insist on the sum function, this also work:
np.sum(np.isnan(m))
Related
My task is to convert one big MATLAB file into python.
There is a line in MATLAB
weightsEI_slow = random('binom',1,0.2,[EneuronNum_slow,IneuronNum_slow]);
I am trying to convert this into python code, I am not quite finding the right documentation. I looked for numpy library too. Does any one have any suggestions?
It looks like you generate a random number that follows the Binomial distribution with probability p=0.2 and sample size n=1. In turn, you can leverage numpy
import numpy as np
np.random.binomial(n=1, p=0.2)
>0
If you require replicability, add np.random.seed(3408) before the number is sampled. Otherwise, the output might be 0 or 1 depending on the execution. Of course, you can switch in another integer value as the seed instead of 3408.
The sum of a standard python list say x=list(range(100000)) does not coincide with a sum of the same sequence x_array=np.array(x). In the first case I obtain sum(x)=4999950000, which is the correct result. Using numpy sum I obtain np.sum(x_array))=704982704. This troubles me because i am a beginner with this language. Does anyone have an explanation for this difference? Thank you. The code is
import numpy as np
x=list(range(100000))
print("sum x using standard python function = ",sum(x))
x_array=np.array(x)
print("sum x using numpy =",np.sum(x_array))
Your NumPy defaults to standard 32-bit integers; Python will switch to indefinitely long integers as needed.
You got bitten by overflow/wraparound.
4999950000 % (2**32) ==> 704982704
Is there some way to make the random number generator in numpy generate the same random numbers as in Matlab, given the same seed?
I tried the following in Matlab:
>> rng(1);
>> randn(2, 2)
ans =
0.9794 -0.5484
-0.2656 -0.0963
And the following in iPython with Numpy:
In [21]: import numpy as np
In [22]: np.random.seed(1)
In [23]: np.random.randn(2, 2)
Out[23]:
array([[ 1.624, -0.612],
[-0.528, -1.073]])
Values in both the arrays are different.
Or could someone suggest a good idea to compare two implementations of the same algorithm in Matlab and Python that uses random number generation.
Thanks!
Just wanted to further clarify on using the twister/seeding method: MATLAB and numpy generate the same sequence using this seeding but will fill them out in matrices differently.
MATLAB fills out a matrix down columns, while python goes down rows. So in order to get the same matrices in both, you have to transpose:
MATLAB:
rand('twister', 1337);
A = rand(3,5)
A =
Columns 1 through 2
0.262024675015582 0.459316887214567
0.158683972154466 0.321000540520167
0.278126519494360 0.518392820597537
Columns 3 through 4
0.261942925565145 0.115274226683149
0.976085284877434 0.386275068634359
0.732814552690482 0.628501179539712
Column 5
0.125057926335599
0.983548605143641
0.443224868645128
python:
import numpy as np
np.random.seed(1337)
A = np.random.random((5,3))
A.T
array([[ 0.26202468, 0.45931689, 0.26194293, 0.11527423, 0.12505793],
[ 0.15868397, 0.32100054, 0.97608528, 0.38627507, 0.98354861],
[ 0.27812652, 0.51839282, 0.73281455, 0.62850118, 0.44322487]])
As Bakuriu suggest it works using MATLABs twister:
MATLAB:
>> rand('twister', 1337)
>> rand()
ans =
0.2620
Python (Numpy):
>>> import numpy as np
>>> np.random.seed(1337)
>>> np.random.random()
0.2620246750155817
One way to ensure the same numbers are fed to your process is to generate them in one of the two languges, save them and import into the other language. This is fairly easy, you could write them in a simple textfile.
If this is not possible or desirable, you can also make sure the numbers are the same by doing the generation of the pseudo random numbers yourself. Here is a site that shows a very simple example of an easy to implement algorithm: Build your own simple random numbers
If the quality of your homemade random generator is not sufficient, you can build a random generation function in one language, and call it from the other. The easiest path is probably to call matlab from python.
If you are feeling lucky, try playing around with the settings. For example try using the (outdated) seed input to matlabs random functions. Or try using different kinds of generators. I believe the default in both languages is mersenne twister, but if this implementation is not the same, perhaps a simpler one is.
How about running a matlab script to get the random numbers based upon a seed, from within your python code?
I am currently writing some code which is supposed to perform FFT on a set of data. I have a python list of points and I can easily create a time list. When I run fft(datalist), I get the 'TypeError: 'numpy.ndarray' object is not callable' error. I think (but please correct me) the issue is that the list is one dimension and they have no attachment to time at all by using that one line of code above. My question is, do I have to input a two dimensional array with time and data points? or am I completely wrong and have to rethink?
Thanks, Mike
Edit - forgot to add some code. The t=time. Could it be because the number of entries in the array isnt equal to 2^n where N is an integer?
sample_rate=10.00
t=r_[0:191.6:1/sample_rate]
S = fft([mylist])
print S
The Numpy and SciPy fft functions are looking to have numpy arrays as input, not native python lists. Also they work just fine with lengths that are not powers of two. You probably just need to cast your list as an array before passing it to the fft.
From your example code above try:
from numpy.fftpack import fft
from numpy import array
""" However you generate your list goes here """
S = fft(array([mylist]))
I get NameError: name 'array' is not defined in python error when I want to create array, for example:
a = array([1,8,3])
What am I doing wrong? How to use arrays?
You need to import the array method from the module.
from array import array
http://docs.python.org/library/array.html
For basic Python, you should just use a list (as others have already noted).
If you are trying to use NumPy and you want a NumPy array:
import numpy as np
a = np.array([1,8,3])
If you don't know what NumPy is, you probably just want the list.
If you need a container to hold a bunch of things, then lists might be your best bet:
a = [1,8,3]
Type
dir([])
from a Python interpreter to see the methods that lists support, such as append, pop, reverse, and sort.
Lists also support list comprehensions and Python's iterable interface:
for x in a:
print x
y = [x ** 2 for x in a]
You probably don't want an array. Try using a list:
a = [1,8,3]
Python lists perform like dynamic arrays in many other languages.
You need to import the array.
from numpy import array
In python Import problem occurs when you accidentally name your working file the same as the module name. This way the python opens the same file you created using the same as module name which causes a circular loop and eventually throws an error.
This question is asked 10 yrs ago , but it may be helpful for late python learners
If you're trying to use NumPy, use this:
import numpy as np
a = np.array([1, 2, 3])
If not then a list is way more easier:
a = [1, 2, 3]
**from array import ***
myarray=array('i',[10,39,48,38])
Maybe you haven´t executed the cell. It worked for me
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