62
votes
5
answers
564
views
What are the differences between numpy arrays and matrices? Which one should I use?
What are the advantages and disadvantages of each? From what I've seen, either one can work as a replace
53
votes
10
answers
2.5K
views
Pandas conditional creation of a series/dataframe column
I have a dataframe along the lines of the below: Type Set 1 A Z 2 B Z
64
votes
18
answers
812
views
Find nearest value in numpy array
Is there a numpy-thonic way, e.g. function, to find the nearest value in an array? Example: np.find_nearest
69
votes
7
answers
441
views
What is the purpose of meshgrid in Python / NumPy?
Can someone explain to me what is the purpose of meshgrid function in Numpy? I know it creates some kind of gr
66
votes
3
answers
414
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
65
votes
8
answers
415
views
Numpy array dimensions
I'm currently trying to learn Numpy and Python. Given the following array: import numpy as np a = np.arr
48
votes
15
answers
435
views
Sorting arrays in NumPy by column
How can I sort an array in NumPy by the nth column? For example, a = array([[9, 2, 3], [4, 5, 6],
60
votes
10
answers
1.8K
views
Pandas read_csv low_memory and dtype options
When calling df = pd.read_csv('somefile.csv') I get: /Users/josh/anaconda/envs/py27/lib/pytho
59
votes
7
answers
2.9K
views
pandas create new column based on values from other columns / apply a function of multiple columns, row-wise
I want to apply my custom function (it uses an if-else ladder) to these six columns (ERI_Hispanic, ERI_AmerInd
55
votes
17
answers
1.5K
views
How to find all occurrences of an element in a list
index() will give the first occurrence of an item in a list. Is there a neat trick which returns all indices i
53
votes
13
answers
929
views
How do I read CSV data into a record array in NumPy?
I wonder if there is a direct way to import the contents of a CSV file into a record array, much in the way th
60
votes
11
answers
1.4K
views
Most efficient way to map function over numpy array
What is the most efficient way to map a function over a numpy array? The way I've been doing it in my cur
47
votes
30
answers
797
views
How to count the occurrence of certain item in an ndarray?
In Python, I have an ndarray y that is printed as array([0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1]) I'm trying
65
votes
5
answers
2.6K
views
What are the advantages of NumPy over regular Python lists?
What are the advantages of NumPy over regular Python lists? I have approximately 100 financial markets series
54
votes
17
answers
1.3K
views
Is there a NumPy function to return the first index of something in an array?
I know there is a method for a Python list to return the first index of something: >>> l = [1, 2, 3]
68
votes
11
answers
1.3K
views
What does -1 mean in numpy reshape?
A numpy matrix can be reshaped into a vector using reshape function with parameter -1. But I don't know w
47
votes
8
answers
1.7K
views
How to access the ith column of a NumPy multidimensional array?
Suppose I have: test = numpy.array([[1, 2], [3, 4], [5, 6]]) test[i] gets me ith line of the array (eg [1,
62
votes
15
answers
747
views
Convert pandas dataframe to NumPy array
I am interested in knowing how to convert a pandas dataframe into a NumPy array. dataframe: import numpy as
51
votes
20
answers
2.3K
views
How do I get indices of N maximum values in a NumPy array?
NumPy proposes a way to get the index of the maximum value of an array via np.argmax. I would like a similar
55
votes
22
answers
833
views
How can the Euclidean distance be calculated with NumPy?
I have two points in 3D: (xa, ya, za) (xb, yb, zb) And I want to calculate the distance: dist = sqrt((xa-xb)^
