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Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.
13
votes
Accepted
Replacing values above a threshold with 1
Use Clip:
Clip[{0.61975, 10562., 0.43274, 0.15068, 0.13703, 0.057564}, {-Infinity, 1}]
{0.61975, 1, 0.43274, 0.15068, 0.13703, 0.057564}
5
votes
Pattern matching - comparing two lists
I assume you want to find an exact match, instead of just that individual members of the subset are found in the larger list. This can be quite easily be accomplished with the following:
ClearAll[sub …
2
votes
How to trim the zeros from the right of a list?
Do you absolutely need a built-in function? At least if performance is not a concern, this is the simplest way to do it:
{0,1,0,0,2,0,0} /. {x___, 0 ..} :> {x}
{0, 1, 0, 0, 2}
This can be writ …
3
votes
Combining two lists taking all possible combinations into account
updatedm = Flatten /@ Tuples[{m, l}]
List-of-lists variant of Tuples does this directly, you just need to flatten (or Apply@Append) entries of l for each element of output to achieve your intended r …
7
votes
Better way to make a certain list with palindromic sublists
The question is in my opinion more about math than Mathematica and so is my answer (unless the goal is to create these lists through specific constructs), but here it is nonetheless:
Table[(1 + x - A …
5
votes
Accepted
Isolating sequences from a list based on a formula
Use PatternSequence, Condition (/;) and a form of Repeated that allows matching zero or one times:
SeedRandom[6];
With[{alist = RandomInteger[{-2, 2}, 200]},
SequenceReplace[alist,
k : {PatternSe …
19
votes
6
answers
1k
views
A clean way to conceptually extract Parts from a circular list
I quite often run into a situation where I want to treat a list as a circular (repeating) list, and want to take a specific sublist of it, such as...
One past the end of the list:
Append[#, First@#] …
9
votes
7
answers
547
views
Efficient deletion of specific list entries
It is sometimes useful to remove exactly the amount of specific entries on one list from another.
Consider:
CountingComplement[{1, 2, 1, 3, 1, 3, 4, 5}, {6, 1, 3, 1, 5}]
{2, 1, 3, 4}
Two 1s a …
6
votes
What's fastest way of defining 10^5 down values?
My solution is ugly, but task-specific. It builds a bitmap out of machine-sized integers in imperative fashion and uses Compile. This works reasonably in memory usage for ranges that have at least cou …
3
votes
Accepted
Calculate Cumulative Mean and Standard Deviation of a list without FOR loops
Turning my comment into an answer:
ClearAll[MapAccumulate];
MapAccumulate[f_, list_List] := f@Take[list, #] & /@ Range@Length@list;
Now you can do stuff like this:
MapAccumulate[Mean, mylist]
12
votes
How to generate all possible orderless partitions of a list according to another list?
It's far from pretty, using pattern matching (OrderlessPatternSequence):
ReplaceList[#1,
Module[{names = Unique[] & /@ #1, partitions},
partitions = Internal`PartitionRagged[names, #2];
Ac …
2
votes
Find duplicates in list of InfiniteLine
RegionEqual, like many region functions, is able to compute symbolic results as long as arguments are fully specified. This allows more efficient constructions of the following kind - where the symbol …
1
vote
Random Matrix with criteria
If we ignore random sampling, this is a simple question of Boolean satisfiability:
Module[{m, n, greens, matrix, sol},
m = 8;
n = 5;
greens = 20;
matrix = Array[c, {m, n}];
sol =
matrix /.
…
32
votes
Accepted
Can Mathematica put these puzzle pieces together?
Assuming polygons follow the same (clockwise or counterclockwise) vertex order, find all good quality two line segment rigid mappings between polygons without overlap with each other (at least much ov …
14
votes
Accepted
Evenly spaced Tick marks for Primes
As people on the comments pointed out this may be a problematic in various ways, but if all y-values of your points are primes, this can be accomplished with ScalingFunctions option. PrimePi is an inv …