Tagged Questions
0
votes
0answers
33 views
Generating partitions of a set with a specified size of the parts [duplicate]
I tried the following (inspired by the answer here)
myList = {a, b, c};
Needs["Combinatorica`"];
SetPartitions[myList]
and I got this answer,
...
12
votes
3answers
221 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 ...
10
votes
3answers
376 views
What is Mathematica's equivalent to MATLAB's filter function?
The MATLAB code
filter(0.5,[1, -0.5], [1:10])
is equivalent to
Rest@FoldList[(#1 + #2)/2. &, 0, Range[10]]
I don't ...
1
vote
2answers
123 views
Select rows from table by keys
I am looking for a way to iteratively select all sublists with the same ID (my 1st column, residual columns are AbsoluteTime entries). First, I obtained the list of ...
0
votes
0answers
62 views
-8
votes
1answer
198 views
Plotting Energies vs. m for all values of R with the colors of the levels indexed by R [closed]
I have two lists like this:
...
0
votes
1answer
61 views
Collecting roots of different equations and create a list
I solve two equations and have two solutions one by each equation. I want to create list of these roots. Could anyone please help me? Appreciate it.
m02R150 = FindRoot[P1 == 0, {E1, 0.07, 0.1}]
...
0
votes
1answer
98 views
Where do those nulls come from? [closed]
I have seen discussions of unwanted nulls in the output in the context of building lists with conditions on the elements, but that is not involved here. I would like to know where the nulls come from ...
8
votes
4answers
271 views
Best way to modify values in a list of rules?
Recently I had to solve a problem similar to this:
Let's say I have a list of list of rules
...
8
votes
4answers
290 views
Passing large list by reference
I have the following problem: I would like to control evaluation of a variable that points to a list. For example, frequently in the code I have functions of the form that are supposed to work on ...
0
votes
1answer
133 views
Find Roots in Do loop
Task: Finding roots in loop
t = List[1, 2, 3, 4, 5]
fx[x_] := a*x^2 - 5
List[Do[Print[FindRoot[fx[k] == 1, {a, 1}]], {k, 0, 5}]]
Output: Currently the output is ...
5
votes
3answers
225 views
Delete elements from a list really fast
I have this bit of code that works, but it's very slow when there are 600k elements in the list:
...
11
votes
8answers
378 views
Any built-in function to generate successive sublists from a list?
Given
lst = {a, b, c, d}
I'd like to generate
{{a}, {a, b}, {a, b, c}, {a, b, c, d}}
but using built-in functions only, ...
1
vote
3answers
211 views
How to create functions of arbitrary number of variables?
In the following code what would be the simplest way to generalize it to say some $N_f$ number of $z$ instead of just $z_1$ and $z_2$?
...
6
votes
3answers
198 views
Filtering elements from a list
Suppose that I have a list
{{{2, 1}, {4, 3}, {2, 4}}, {{2, 1}, {4, 3}, {3, 1}},
{{2, 1}, {2, 4}, {3, 1}}, {{4, 3}, {2, 4}, {1, 2}}}
I want to make a new list ...
2
votes
1answer
113 views
Computing closest set of points to each point in large set — running out of memory (arrays unpacking)
I have a large set of points in 3D and I'm trying to identify all the points that lie within a certain distance of each point. Then using this data store the vector between the pairs of points.
I ...
4
votes
1answer
192 views
speed up iteration with conditionals plus optimize memory usage
Given list1 and list2 whose elements are vectors of a certain (fixed) dimension, I am interested in the behaviour of a scalar ...
4
votes
4answers
173 views
clean functional way to get first n rows that yield maximum rank
I have a matrix A and want the matrix consisting of the first n rows of A, having the same rank as A, where n is minimal.
More generally, I want the shortest "start piece" of a list, such that some ...
3
votes
2answers
406 views
Optimize inner loops
I'm Mathematica newbie so please be gentle :)
I have this, heavily non-optimized part of code, which I would like to speed up. I have put all matrices to be RandomReal, but in my code they take ...
2
votes
1answer
123 views
Why is MapIndexed better than mapping over a range?
Background
I'm working on an application in which I need to create and control two sets of locators. I know from reading the Mathematica documentation and certain posts on Mathematica.SE that this ...
7
votes
3answers
203 views
Restricted accumulation of values
Please consider the following list data. I was trying to accumulate data until the result turns positive the first time and ...
4
votes
3answers
278 views
4
votes
2answers
190 views
How can I use Max[] in a function that is passed a list not find the max of the list
For most functions in Mathematica, passing them a list will call the function on each element of the list. For example:
...
19
votes
3answers
321 views
How can I regroup elements in a list into a tree based on their values?
I have a list of elements in an outline, here is an example that is only 3 levels deep:
...
18
votes
11answers
639 views
Generating an ordered list of pairs of elements from ordered lists
I have a pair of ordered lists. I want to generate a new ordered list (using the same ordering) of length n by applying a binary operator to pairs of elements, one from each list, along with the index ...
7
votes
2answers
270 views
find subsequences of constant increase
A list like
l = {0, 1, 2, 3, 4, 5, 7, 9, 12, 13, 18, 19}
may have subsequences of constant increase, $a_{n+1} = a_n + k$.
For example:
...
10
votes
3answers
267 views
Generating Linear Extensions of a Partial Order
Given a set $S$ and a partial order $\prec$ over $S$, I'm looking for a way to "efficiently" generate a list of linear extensions of $\prec$. Suppose the partial order is given by a ...
18
votes
6answers
811 views
5
votes
1answer
223 views
How to monitor the progress of Map?
I have a function doSomethingComplicated[...] that takes about 10s on average to evaluate. My list, listOfArgs has about 10000 ...
13
votes
3answers
2k views
K-means clustering
In MATLAB, there is a command kmeans() that divides an array into $k$ clusters and calculates the centroid of each cluster.
Is there any command in Mathematica to ...
14
votes
4answers
365 views
Implementing a function which generalizes the merging step in merge sort
One of the key steps in merge sort is the merging step. Given two sorted lists
sorted1={2,6,10,13,16,17,19};
sorted2={1,3,4,5,7,8,9,11,12,14,15,18,20};
of ...
9
votes
1answer
273 views
Modifying a List in a function in place
An example will be most specific:
func[list_, column_] := list[[All, column]] = Map[#*2 &, list[[All, column]]];
This throws errors.
I want to avoid doing ...
4
votes
1answer
250 views
Path queries for tree-structured data
Can anyone suggest documentation or tutorials for developing path queries and indices for (XML-like) tree-structured data?
Suppose data is organized hierarchically in key->value pairs, eg:
...
15
votes
1answer
220 views
Are there advantages to using additional arguments of common functions rather than alternative ways of calculating with lists?
(Apologies for the long question title.)
One of the interesting, if sometimes confusing, things about Mathematica is that there is always more than one way to do things. Even intermediate users can ...
8
votes
7answers
279 views
How to efficiently Append a result of an operation on each element of a list to itself
I'm looking for the best function to apply the product of the last two elements of sublist elements to each element:
Example:
...
7
votes
5answers
309 views
How to distinguish between lists and values?
I have a (hopefully small) problem with some numerical integration algorithm, more specifically I want to integrate the imaginary part of a complex valued function, e.g. ...
13
votes
5answers
957 views
Finding all elements within a certain range in a sorted list
Suppose we have a sorted list of values. Let's use list = Sort@RandomReal[1, 1000000]; for this example.
I need a fast function ...
12
votes
6answers
555 views
Splitting up delimited data in lists
One task that I frequently find myself doing in Mathematica is splitting lists into lists of sublists, using specific elements to define the break-points. This is particularly useful with imported ...
12
votes
9answers
411 views
Generating a matrix using sublists A and B n times
I want to write a function that generates a square matrix from sublists. My sublists are
a = Range[0, x, 0.5]; b = Range[0.25, x + 0.25, 0.5];
Suppose x=2, then I ...
