All Questions
31 questions
-1
votes
3
answers
117
views
How can I get a sublist with wraparound in Python
Simple 1D case
I would like to get a substring with wraparound.
str = "=Hello community of Python="
# ^^^^^ ^^^^^^^ I want this wrapped substring
str[-7]
> 'P'
str[5]...
- 1,764
0
votes
0
answers
200
views
Extract labels for generated sequences
I am trying to create sequences from a labeled dataset of transactions. The labels are 1 for "fraudulent" and 0 for "genuine", and the label column is called: 'is_fraud'.
First, I ...
- 149
0
votes
1
answer
61
views
How to extract a new array after skipping a certain number of items in the array repeatly using numpy
num_pixels_per_cell_one_axis = 4
num_cells_per_module_one_axis = 4
inter_cell_sep = 2
max_items_in_list = num_cells_per_module_one_axis * num_pixels_per_cell_one_axis + (num_cells_per_module_one_axis-...
- 17
1
vote
1
answer
695
views
slicing python list beyond its length
I have to slice a Python list/numpy array from an index to -dx and +dx.
where dx is constant. for example:
(the position/index that contains 1 only for illustration, as the center index).
A = [0, 0, 0,...
- 111
-2
votes
1
answer
191
views
Formatting columns of multidimensional arrays into 1D arrays [duplicate]
I want to access right side of the 2D array. I would like to turn the second column into a 1D array 4883,4967,4968... . I tried doing list_[len(list_),1] however that doesn't work. How would I be able ...
- 687
2
votes
1
answer
146
views
Replacing list comprehensions with pandas and numpy Python
The function below uses slices to get the maximum value between 2 indexes at once. So it gets the maximum value between 0 and 10 and then 10 and 12 and such. The function is derived from the answer to ...
- 687
1
vote
2
answers
87
views
Is it possible to slice multidimensional LISTS (not numpy) in python?
This question is the same as this one, but for native python lists.
Assume the following:
import numpy as np
a = np.ones((5, 6, 7))
a_list = a.tolist()
I can slice a like so:
a_slice = a[2:4, 4:, :3]
...
- 27.7k
0
votes
1
answer
827
views
Slice list with numpy array
I have a list, lets say:
list = ['A1', 'A2', 'A3']
I have some data, that returns with an Numpy array of either:
array([0])
array([1])
array([2])
Which are indicating the index of the corresponding ...
0
votes
1
answer
435
views
Match along last axis in numpy array
I saw a lot of articles and answers to other questions about slicing 3D lists in python, but I can't apply those methods to my case.
I have a 3D list:
list = [
[[0, 56, 78], [4, 86, 90], [7, 87, ...
- 35
1
vote
1
answer
1k
views
Python Underscore Inside List
I realize that underscores are used for a number of cases, such as throwaway variables in python.
I recently came across the following example:
a = [1, 2, 5, 3]
a[_]
Now the second line returns a ...
- 121
0
votes
1
answer
158
views
Why is this Python array not slicing?
Initial data is:
array([[0.0417634 ],
[0.04493844],
[0.04932728],
[0.04601787],
[0.04511007],
[0.04312284],
[0.0451733 ],
[0.04560687],
[0.04263394],
[0.04183227],
[0....
- 29
1
vote
0
answers
642
views
Slicing to an offset from the end of an array, where the offset may be 0
I'd like to slice an array with an offset from the end, but I'd like to be able to potentially include the end.
import numpy as np
a = np.arange(10)
b = np.zeros_like(a)
for i in range(10):
b[:-...
- 191
1
vote
1
answer
158
views
Slice an array with a list of indices
Suppose a = array([1,2,3]) and b = array([4,5,6]). I want to slice a and b using a list and perform some operation on each part, then return the result to an array. For example i propose a dummy ...
- 899
3
votes
4
answers
13k
views
How to remove empty element from numpy array
Here an example:
a = np.array([[1, 2, 3,4], [], [1,2,0,9]])
print(a)
# array([list([1, 2, 3, 4]), list([]), list([1, 2, 0, 9])], dtype=object)
How to remove the empty element and return only:
...
- 1,750
-1
votes
1
answer
30
views
Need to understand what is the use of [::-1] in the code? [duplicate]
I tried to remove the part I got the result but only in reverse order. So my question here is that why are we using that part to splice the array.
import numpy as np
import cv2
img = cv2.imread("E:/...
3
votes
1
answer
4k
views
Slicing a numpy array to select rows with values in a list. Truth value error
I have a 2D numpy array, and I wish to select rows that have a specific value in a given column. This is simple enough to do with single numbers or multiple numbers, but I cannot do it for a list. ...
- 877
3
votes
3
answers
90
views
Manual slicing of a list using their indices, Python
Minimal example
I have a list a = [10,20,30,40,50,60,70,80,90,100,110,120,130,140,150,....,]
I want to get a new list new_list = [40,50,60,100,110,120,...], i.e. append fourth, fifth and sixth value,...
- 9,363
0
votes
3
answers
270
views
Selecting elements from list of two arrays
I have the following list of two arrays:
l=[array([16, 19]), array([24, 17])]
How one make new lists to have
#[16,24] and [19,17]
I have tried l[0] and l[1] but those just give me [array([16, 19]...
- 47
5
votes
3
answers
20k
views
what does [::-1] mean in python - slicing?
I have a variable a=range(0,5) and i need to know why and how a[::-1] this works. The answer i am getting is range(4,-1,-1). Thanks for help.
P.S. It is quite a basic question but as this question ...
- 180
4
votes
2
answers
2k
views
How can I slice a list to get every 2 consecutive elements of the list in new lists?
Say you have a list [1,2,3,...,99,100]
import numpy as np
ls = np.linspace(1,100,100)
Say you fiddle around with the slice notation to find ones that works for you.
print(ls[:2])
>> [ 1. 2.]...
user7345804
4
votes
5
answers
2k
views
Slicing sublists with different lengths
I have a list of lists. Each sublist has a length that varies between 1 and 100. Each sublist contains a particle ID at different times in a set of data. I would like to form lists of all particle IDs ...
- 131
0
votes
1
answer
6k
views
For an array a and b in Python, what is the code a[b[0:2]] is actually trying to do?
Could somebody please help on explaining the meaning of this error message?
There is this part of lines of code that I am trying to understand. So I experimented myself with an easier example.
I ...
- 723
3
votes
6
answers
2k
views
Python/Numpy fast way to selecting every nth chunk in list
Edited for the confusion in the problem, thanks for the answers!
My original problem was that I have a list [1,2,3,4,5,6,7,8], and I want to select every chunk of size x with gap of one. So if I want ...
3
votes
2
answers
4k
views
if statement whilst slicing
I have a number of lists that I am slicing, such that (using example data):
midpoint = [[0.2], [0.5], [0.6]]
Values = [[0.1, 0.3, 0.6, 0.8], [0.2,0.3,0.5,0.7], [0.2,0.5,0.6,0.9]]
numbers = numpy....
- 1,665
1
vote
1
answer
359
views
How to efficiently slice a Python list into chunks of 20 + a slice for the remainder? [duplicate]
Given a list of URLs urls of unknown length, I want to divide it into slices of 20 urls (plus the slice containing the remainder, if there is one). So if it contains 96 URLS, I'll have a 4 slices of ...
- 16.1k
0
votes
1
answer
120
views
Python - Iterating through list of list as a matrix (slice)
I want to iterate through list of list.
To iterate through every list inside list also.
list=[[0.9 0.8 0.1 0.2 0.5 ][0.5 0.3 0.2 0.1 0.7 ][0.6 0.1 0.3 0.2 0.9][0.3 0.7 0.4 0.1 0.8]]
Thus to iterate ...
- 11
1
vote
3
answers
1k
views
Slice away first element in each (list) element in a list in Python
Say we have a list:
a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Then I want to create a new list through slicing away the first element in each element in the list:
b = a[][1:]
Obviously the above doesn'...
- 1,035
17
votes
2
answers
9k
views
Python Slice Notation with Comma/List
I have come across some python code with slice notation that I am having trouble figuring out.
It looks like slice notation but uses a comma and a list:
list[:, [1, 2, 3]]
Is this syntax valid? If ...
- 17.9k
6
votes
2
answers
12k
views
Converting nested lists of data into multidimensional Numpy arrays
In the code below I am building data up in a nested list. After the for loop what I would like is to cast it into a multidimensional Numpy array as neatly as possible. However, when I do the array ...
- 952
13
votes
4
answers
10k
views
Python lists/arrays: disable negative indexing wrap-around in slices
While I find the negative number wraparound (i.e. A[-2] indexing the second-to-last element) extremely useful in many cases, when it happens inside a slice it is usually more of an annoyance than a ...
- 361k
85
votes
3
answers
65k
views
Python Array Slice With Comma?
I was wondering what the use of the comma was when slicing Python arrays - I have an example that appears to work, but the line that looks weird to me is
p = 20*numpy.log10(numpy.abs(numpy.fft.rfft(...
- 1,269