Questions tagged [numpy]
NumPy is one of the many modules in Python that adds support of large multidimensional arrays and matrixes, along with a large library of high-level mathematical functions for operations with these arrays.
numpy
13,252
questions
500
votes
14
answers
847k
views
How do I create a new column where the values are selected based on an existing column?
How do I add a color column to the following dataframe so that color='green' if Set == 'Z', and color='red' otherwise?
Type Set
1 A Z
2 B Z
3 B X
4 C Y
- 33.7k
369
votes
27
answers
429k
views
Split (explode) pandas dataframe string entry to separate rows
I have a pandas dataframe in which one column of text strings contains comma-separated values. I want to split each CSV field and create a new row per entry (assume that CSV are clean and need only be ...
- 17.3k
408
votes
11
answers
1.8m
views
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
Let x be a NumPy array. The following:
(x > 1) and (x < 3)
Gives the error message:
ValueError: The truth value of an array with more than one element is
ambiguous. Use a.any() or a.all()
How ...
- 67.4k
214
votes
18
answers
127k
views
Cartesian product of x and y array points into single array of 2D points
I have two numpy arrays that define the x and y axes of a grid. For example:
x = numpy.array([1,2,3])
y = numpy.array([4,5])
I'd like to generate the Cartesian product of these arrays to generate:
...
- 12.5k
260
votes
20
answers
183k
views
Find unique rows in numpy.array
I need to find unique rows in a numpy.array.
For example:
>>> a # I have
array([[1, 1, 1, 0, 0, 0],
[0, 1, 1, 1, 0, 0],
[0, 1, 1, 1, 0, 0],
[1, 1, 1, 0, 0, 0],
[...
- 85.2k
688
votes
11
answers
1.1m
views
Most efficient way to map function over numpy array
What is the most efficient way to map a function over a numpy array? I am currently doing:
import numpy as np
x = np.array([1, 2, 3, 4, 5])
# Obtain array of square of each element in x
squarer = ...
- 8,091
707
votes
16
answers
1.7m
views
Convert pandas dataframe to NumPy array
How do I convert a pandas dataframe into a NumPy array?
DataFrame:
import numpy as np
import pandas as pd
index = [1, 2, 3, 4, 5, 6, 7]
a = [np.nan, np.nan, np.nan, 0.1, 0.1, 0.1, 0.1]
b = [0.2, np....
- 7,087
631
votes
8
answers
1.3m
views
Create new column based on values from other columns / apply a function of multiple columns, row-wise in Pandas
I want to apply my custom function (it uses an if-else ladder) to these six columns (ERI_Hispanic, ERI_AmerInd_AKNatv, ERI_Asian, ERI_Black_Afr.Amer, ERI_HI_PacIsl, ERI_White) in each row of my ...
- 7,280
570
votes
7
answers
253k
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, and I am going to create a cube array of 100x100x100 = 1 million cells. I will be ...
- 24.5k
215
votes
12
answers
1.2m
views
python numpy ValueError: operands could not be broadcast together with shapes
In numpy, I have two "arrays", X is (m,n) and y is a vector (n,1)
using
X*y
I am getting the error
ValueError: operands could not be broadcast together with shapes (97,2) (2,1)
When (97,2)x(2,...
- 7,986
201
votes
4
answers
273k
views
Binning a column with pandas
I have a data frame column with numeric values:
df['percentage'].head()
46.5
44.2
100.0
42.12
I want to see the column as bin counts:
bins = [0, 1, 5, 10, 25, 50, 100]
How can I get the result as ...
- 21.1k
17
votes
2
answers
5k
views
Python: Justifying NumPy array
Please I am a bit new to Python and it has been nice, I could comment that python is very sexy till I needed to shift content of a 4x4 matrix which I want to use in building a 2048 game demo of the ...
- 307
211
votes
10
answers
265k
views
Using NumPy to build an array of all combinations of two arrays
I'm trying to run over the parameters space of a six-parameter function to study its numerical behavior before trying to do anything complex with it, so I'm searching for an efficient way to do this.
...
- 13.9k
800
votes
26
answers
1.5m
views
How can the Euclidean distance be calculated with NumPy?
I have two points in 3D space:
a = (ax, ay, az)
b = (bx, by, bz)
I want to calculate the distance between them:
dist = sqrt((ax-bx)^2 + (ay-by)^2 + (az-bz)^2)
How do I do this with NumPy? I have:
...
- 126k
140
votes
9
answers
86k
views
How do you fix "runtimeError: package fails to pass a sanity check" for numpy and pandas?
This is the error I am getting and, as far as I can tell, there is nothing useful on the error link to fix this.
RuntimeError: The current Numpy installation
('...\\venv\\lib\\site-packages\\numpy\\...
- 1,403