Questions tagged [list-manipulation]
Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.
529
questions with no upvoted or accepted answers
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answers
411
views
Strategies to find curves on messy data using FindCurvePath
I have a set of data points that correspond to roots of a transcendental equation with respect to a parameter (the abscissa) which, by the properties of the system, define continuous curves (might be ...
- 1,589
12
votes
0
answers
120
views
What changed in String handling between 11.0 and 11.3?
I was trying to optimize some String-handling code here using my standard trick of converting it to a list of bytes first and using basic list operations instead of ...
- 45.8k
10
votes
0
answers
266
views
Visualising 'The Moessner Miracle' in higher dimensions
I thought it would be interesting to try and represent "The Moessner Miracle" in higher dimensions. This is my first attempt for higher dimensions anywhere so I'm not sure if the logic is ...
- 974
10
votes
0
answers
78
views
Different timing with large array assignment
Consider the following example
n = 10^8;
AbsoluteTiming[
A = ConstantArray[1., n]; // anyFunc;
A[[2 ;; ;; 2]] = -1.;
]
{0.388108, Null}
...
- 6,675
9
votes
0
answers
106
views
Predicting Pick performance
I'm trying to figure out how to use Pick most efficiently. I use it already in a number of places, but only ever in the context of ...
- 45.8k
8
votes
0
answers
164
views
About efficiency of modifying large list in place
In Wagner's book "Power Programming with Mathematica" page 303. Wagner metioned do not "modify large list in place"
He take two example
...
- 16.4k
6
votes
0
answers
261
views
How to create a prefix code
I am trying to create a demonstration of shannon code in mathematica.
Given a list of lengths (l1, l2,..lk) I need to create a list of binary lists (or list of ...
- 205
6
votes
0
answers
231
views
Bug in ListLinePlot[] when Filling up and down?
Bug introduced in 9.0 or earlier and persisting through 13.0.0 or later
I'm trying to understand this apparently incorrect Filling behavior in ...
- 1,456
5
votes
0
answers
106
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5
votes
0
answers
81
views
Join on QuantityArray
I need to merge two QuantityArray objects of mixed type. My first attempt looks something like:
...
- 45.8k
5
votes
0
answers
101
views
SimilarityRules for SequenceAlignment of two lists
I am trying to use the SimilarityRules option of SequenceAlignment to customize its output. This works perfectly for strings, ...
- 680
5
votes
0
answers
758
views
How to extract structured array data from DefineDLLFunction in Mathematica
I want to use my Bluechip PCI-ADC acquisition card in Mathematica via his dynamic link library “Bcdll32.dll”; (used to access functions on my PCI data acquisition cards). My problem is the function “...
- 121
4
votes
0
answers
161
views
Inconsistent Output Bug and Code-Quits-Kernel Bug with Compile
This is the strangest bug I've encountered. In my experience, variations in the code will unexpectedly crash the kernel, give inconsistent output, or produce expected results with no problems.
1) Code-...
- 1,577
4
votes
0
answers
72
views
Fastest way to change the values of an association
I have an association of the following form :
assoc = Association[a -> {1, 2, 3}, b -> {5, 6, 7}]
<|a -> {1, 2, 3}, b -> {5, 6, 7}|>
(the size ...
- 912
4
votes
0
answers
147
views
4
votes
0
answers
89
views
Why does Shortest not work inside SequencePosition?
Why does Shortest not work in a SequencePosition call? The following two commands return the same answer:
...
- 38.1k
4
votes
0
answers
63
views
Speeding up MovingMap of Dot
I have the following code (showing an insignificant simplification) that I really need to run many times for different ps (its length can be 10^7 or so) and wSize. Is there a way to speed this up ...
- 167
4
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0
answers
274
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4
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0
answers
335
views
Extract a key from an Association?
I have some large nested expression containing associations and I'd like to extract the nth key inside one of them, using part syntax.
Here's a tiny example:
...
- 30.8k
4
votes
0
answers
165
views
How to make reading from long lists faster?
Background
I am using Mathematica to solve a traveling-salesman-like problem. I implemented two different algorithms that are able to solve this type of problem and both algorithms yield the same ...
- 131
4
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0
answers
118
views
How to deal with "Compile::cset" in Compile
When compiling below code
Compile[{{data, _Integer, 2}}, Fold[Flatten /@ Flatten[Outer[List, ##, 1], 1] &, data]]
I encountered error messages
Compile::...
- 16.4k
4
votes
0
answers
108
views
`Optional` with non-empty list requires PatternTest/Condition?
Arbitrary lists are easy to use with Optional:
a[0]~MatchQ~a[0, Optional[x_List, {}]]
a[0]~MatchQ~a[0, Optional[x:{___}, {}]]
...
- 5,619
4
votes
0
answers
98
views
Why isn't SparseArray working in this case?
This works:
SparseArray[{{1, 1} -> 1, {2, 2} -> 2}]\
(* {{1, 0}, {0, 2}} *)
This works:
...
- 1,581
4
votes
0
answers
2k
views
Speed differences between Table, Replace, Array, Map, and AssociationMap
EDIT: Actually, it looks like part of this is bogus—Array doesn't actually work on this input (I'm often a little shaky on what kind of input, exactly, works for ...
- 1,042
4
votes
0
answers
96
views
Create an adequate 'training set' to train a ClassifierFunction which performs the role of the built-in `SubsetQ`
I am trying to "grow" my own SubsetQ function using Machine Learning methods. My cSubsetQ when given two lists (listA and listB)...
- 7,104
4
votes
0
answers
183
views
ParallelTable and expensive functions
I would like to build up a 2D-Table using ParallelTable as follows
...
- 741
4
votes
0
answers
180
views
Gather dependency on list order?
I get intrigued about Gather behavior on this post.
I thought that Gather was invariant under list order?
Here is the result I ...
- 25.6k
3
votes
0
answers
46
views
Operating on a nested list
A very short version of my list named "fire" is
fire = {{0, 0, 0, 20, 0, 0}, {0, 0, 0, 20, 0, 0}, {0, 0, 20, 20, 0, 0}}.
For the first sublist ...
- 31
3
votes
0
answers
72
views
Fastest Way to make rows and columns zero and corresponding (i,i) element 1 of a large Sparse Matrix
I have a 5552 by 5552 sparse matrix:
...
3
votes
0
answers
60
views
Transpose[m,{1,1}]
According to the documentation, Transpose with a second argument {1,1} on a square matrix returns the diagonal of the matrix.
...
- 1,603
3
votes
0
answers
103
views
Sowing Once into Each of Many Lists – Any Better than Append?
In general
I know to try to use Reap and Sow over Append or AppendTo due to superior performance. However, Reap and Sow are notorious for being difficult to understand how to use and how they work ...
- 1,577
3
votes
0
answers
52
views
Why is doing a computation inside Select slower than a precomputation?
I am trying to generate primitive Pythogorean triples using Euclid's parametrization. I basically want a list of pairs with ordered pairs $(m,n)$ such that $m$ and $n$ are coprime.
My first approach ...
- 161
3
votes
0
answers
74
views
Why is ContainsOnly so slow for checking a list is full of zeros?
I'm on Windows 10 Mathematica 12.1.1.
I would expect allocating a big ConstantArray and comparing would be slower but apparently it is not:
...
- 20.6k
3
votes
0
answers
49
views
Bags don't work in parallel code?
Appending to a list in parallel works:
b = {};
SetSharedVariable[b]
WaitAll[Table[ParallelSubmit[{p}, AppendTo[b, 1]], {p, 3}]];
(* b is now {1,1,1} *)
But ...
- 30.8k
3
votes
0
answers
63
views
Net layer that replicates last element
I am trying to design a neural network layer that takes in an array of dimensions n x 100, and produces an array of dimensions ...
- 3,584
3
votes
0
answers
72
views
How can I prevent ParallelTable[] from freezing?
I have spent some time trying to figure this out.
I have a function that appears to be the reason my program is freezing. I am using both MemoryConstrained[] and <...
- 1,397
3
votes
0
answers
72
views
Strange behaviour with Differences
I have some problems with the built-in function Differences. I do not understand how its behaviour comes about under the following circumstances:
...
- 1,171
3
votes
0
answers
1k
views
Is it possible to reshape with one unknown dimension in Wolfram?
In Python I can reshape array remaining one dimension unknown, allowing Python to infer it automatically:
...
- 725
3
votes
0
answers
246
views
Finding possible lattice planes of a crystal structure
After generating a crystal structure from a crystallographic data and duplicating it to a larger crystal system I would like to find possible lattice planes of this crystal.
It is well-known that the ...
- 31
3
votes
0
answers
73
views
Can a simple Part expression produce a list of elements from nested lists?
If list1d is a simple 1-d list, then list1d[[{i, j, k}]] evaluates to a list consisting of the ...
- 11.5k
3
votes
0
answers
65
views
Applying a function along the desired dimensions of a n-dimensional array
I am trying to apply an arbitrary function f that takes several inputs and returns a scalar along some specific dimensions of an n-dimensionnal array.
Here is an ...
- 31
3
votes
0
answers
76
views
Incrementally building a list without memory overhead
I have a task, where I have to combine pairs with a function, but the number of pairs I actually need is much smaller than the number of all pairs. The condition to keep the element is some function ...
- 141
3
votes
0
answers
57
views
Test which symbol of a list depend on some variable
Given a list of symbols, say {y[x],z[x],k}
Is there a way to sort which depend on x and which don't ?
Applied to the above list,...
- 453
3
votes
0
answers
59
views
Map entries of StructuredArray
I have the following defintion
arr = SymmetrizedArray[{1, 2} -> 1, {4, 4}, Antisymmetric[{1, 2}]]
which gives a ...
- 941
3
votes
0
answers
100
views
How to ArrayFlatten some matrix which have repeated element
I have many such matrices(whose dimension are all 3*3.) like:
...
- 24.6k
3
votes
0
answers
55
views
How does ContourDetect work for arrays?
By the Wolfram Documentation, ContourDetect gives a binary sparse array in which 1 corresponds to zeros and zero crossings in an array. However, in the example:
...
- 239
3
votes
0
answers
100
views
3
votes
0
answers
69
views
How to specify alignment of columns when exporting a table using Export, and how to use spaces instead of tabs?
I have a table in list representation. How can I export it, specifying that some columns must be right-aligned and others left-aligned?
Morevoer, columns should be space-separated (with an appropriate ...
- 10.8k
3
votes
0
answers
95
views
Choosing a List as VertexWeight for a TreeGraph
I would like to map every vertex of my TreeGraph to an List.
...
- 31
3
votes
0
answers
695
views
Taking real and imaginary parts of indexed functions and speeding up ComplexExpand
I am setting up a large system of ODEs and in order to use the IDA method (which is sig. faster for my system and thus attractive), I must split my equations into real and imaginary parts.
I am ...
- 349