Linked Questions
18 questions linked to/from Why is there no PositionFunction in Mathematica?
596
votes
19
answers
154k
views
Where can I find examples of good Mathematica programming practice?
I consider myself a pretty good Mathematica programmer, but I'm always looking out for ways to either improve my way of doing things in Mathematica, or to see if there's something nifty that I haven't ...
47
votes
3
answers
2k
views
Why is the new PositionIndex horribly slow?
This issue has largely been mitigated in 10.0.1. New timings for the final test below are:
...
- 269k
20
votes
4
answers
2k
views
Accessing list elements by name
First, a bit of a long introduction to my problem:
I only have a few weeks of Mathematica experience. I am creating a mathematica application that calculates some material properties of steel based ...
- 305
18
votes
7
answers
1k
views
10
votes
7
answers
962
views
intersection between two 2D arrays with labeled data is slow
Here is how to Generate data
the function is below with two images to generate data
img1
img2
...
- 8,860
7
votes
6
answers
487
views
Total by a criteria
I am developing a weighted KNN algorithm. In a step, I need to do the sum of weights of each class. For example:
...
- 1,976
14
votes
3
answers
464
views
Head of a MatrixForm expression?
An example in http://www-zeuthen.desy.de/theory/capp2005/Course/hahn/mathematica.pdf amounts to the following
...
- 11.7k
8
votes
4
answers
2k
views
efficient way to give nearest neighbour and next nearest neighbour of every point in a point set
Suppose we have a point set, the points are labeled 1,2,3,....n. And p[i] is the coordinate of the point. Now I want the label of nearest and next nearest point (...
- 16.9k
9
votes
6
answers
431
views
Truncating a list once all members of a set have appeared?
Consider if you would the case where we have some list of elements:
list0 = {54, 4, 7, 9, 3, 54, 4, 20, 2, 456, 2, 3};
And we have some target list:
...
- 93
3
votes
6
answers
296
views
Change sublist based on position
Supposed that:
list = {2, 3, 5, 7, 9};
sublist = {{3, 3, 5}, {2, 2, 2, 7, 9}};
I want to change each sublist in sublist as following:
Find the positions of ...
- 251
11
votes
2
answers
468
views
Held keys in associations
Bug introduced in 10.0 and persisting through 11.0.1 or later
Bug introduced in 10.0 and fixed in 10.4
Association is new in 10.0.
Bug still present: ...
- 269k
3
votes
3
answers
1k
views
Use map on a different level
I have just started to get used to Mathematica's Map, Apply, and related functions, and I can't figure out how to do maps that require working "one level down".
For example, I am currently trying to ...
- 1,030
11
votes
1
answer
315
views
Dispatch not behaving like a normal expression in Mathematica 10
In Mathematica 9, I used to be able to do
rules = Dispatch[{'a' -> 1, 'b' -> 2}]
rules[[1]]
to extract the rules from ...
- 627
6
votes
2
answers
250
views
What is the fastest way to get a list of subexpressions and their positions?
I have spent quite some time trying to figure out what the fastest way is to get a list lists of all subexpressions and their positions. I have tried things with MapIndexed, which seems ideal in cases ...
- 12.2k
9
votes
1
answer
620
views
Performance of Dispatch and lists of Rules
The issue outlined here seems to be no longer present in version 10, if you use a Dispatch table! This because a Dispatch table ...
- 12.2k