Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.

learn more… | top users | synonyms (3)

12
votes
3answers
347 views

Taking Top K Occurrences

Having millions of numbers in a list, I want to take top K occurrences. MMA Commonest is very slow so I write my own versions: ...
5
votes
3answers
225 views

Split list of states by run lengths and discontinuous changes in state

I was asked to look into writing some simulation code for a user, where the simulation output (x) would oscillate between three possible states: ...
6
votes
1answer
313 views

Stacked Line Graph with fragmented data

Let's start with what I already found on the internet: ...
0
votes
0answers
77 views

How to save the results in an identical Excel file (.xls) in each iteration of a Do loop

Assume the following code (Below code is just an example to clearly illustrate my problem): ...
1
vote
3answers
141 views

How to make list plot when all information is in a single list

I want to make a plot , where the data is structured like so { {"l1", "l2"}, n1, n2, n3} } The values in the inner sub list are labels which are associated with ...
0
votes
0answers
37 views

Filter sublists that contain a certain value [duplicate]

This question is a followup from appending elements to sublist mergedList = { { {"a","b"}, -1.5, -5, "no" }, { {"c","d"}, -2,-10, 7 } } I ...
0
votes
1answer
58 views

If statements with a Boolean [duplicate]

If I have a vector {1,2,3}, I want to write an If statement, where if one of the positions is "1", it will perform a certain command. ...
2
votes
3answers
147 views

appending element to sub list [duplicate]

I have a list of the form: lstA = { { {"a","b"}, -1.5}, { {"c","d"}, -2 } } I wanto to add another value to each sublist that ...
2
votes
1answer
137 views

Multiple swapping of rows and columns

m={{a, b, c, p}, {d, e, f, x}, {g, h, k, z}, {u, v, w, y}}; I want to swap 1st and 2nd rows by 4th and 3rd rows respectively. And then, swap 1st and 2nd columns ...
3
votes
4answers
138 views

Comparing Positions of Elements in a List

How can I check if Position[i] > Position[j] for two arbitrary elements in a given list? The problem is that Position[i] ...
0
votes
0answers
71 views

Improving a function that filters each table from a list of tables

I have written the following function which can take in a list of tables as an arguement, and then filters each one. The function I wrote is below, and the commands I combined are listed below the ...
4
votes
3answers
205 views

Conditional search along the columns of a matrix

I want to implement the following algorithm in Mathematica. Get element along main diagonal of a matrix. If the element along the main diagonal is positive, then return the positions of the elements ...
5
votes
4answers
289 views

Breaking a sorted list into bins of a specified size

Can somebody please explain me the following: If I try to split data every increase in 0.5: ...
0
votes
1answer
61 views

Change input variable in a function [duplicate]

I'd like to write a function, that would take a matrix as an input parameter and would change it by multiplying one of its rows by a factor. I try to do it in the following way: ...
0
votes
0answers
43 views

Plot two functions of two variables against each other [duplicate]

I have two functions f1(n,m) and f2(n,m) but the issue is that f1 generates many values say ...
3
votes
1answer
130 views

Plotting with ColorFunction -> GrayLevel - no black

This is probably a fairly trivial question, yet I have been unable to find an answer - help would be much appreciated! :) I am trying to plot a 28 x 28 matrix (tabulated data given here), containing ...
0
votes
2answers
84 views

adding a 1 to all second elements

I want to add 1 to all second elements but I am running into a "level" problem I believe here is my code: ...
0
votes
1answer
86 views

Generating all “from n choose k” configurations of a simple list [closed]

Suppose that I have a 1-D list called myList. Here's an example: myList = {"A", "B", "C", "D"}; I want to write (or find ...
3
votes
4answers
91 views

Subtracting list from list of same dimensions [duplicate]

This might seem like a basic operation I have already searched for similar answers but found none. I want to subtract the second elements of my list ct from the corresponding element in lt, and ...
4
votes
1answer
144 views

On elegant use of Inner and Outer on tensors

I have a collection of 5-element vectors each of which corresponds to an {x,y} location from a (20 x 21) grid. Because of that I represent that data as a (5 x 20 x 21)-sized tensor called ...
2
votes
2answers
332 views

Get positions of all non zero matrix elements

I want to find all non zero elements of a table and I want to create a list that contains the name of the table the element was removed from, the position of the element, and the value of the element. ...
6
votes
3answers
216 views

Accumulate second elements in sublist

I want to accumulate the second elements in each sublist identified by its first element. ...
0
votes
1answer
71 views

Sum similar elements [closed]

I am interested in summing elements in a list or sublist that are similar. I want the sublists of my second elements to be added cumulatively only if their first elements are the same. This is my ...
6
votes
1answer
126 views

Path construction using `Nearest` shows ill behavior?

I have a dataSet that I'm trying to sort choosing a starting point and going to its nearest neighbor, and then to its nearest neighbor and so on. To do so, I've ...
1
vote
2answers
49 views

List operation on specific elements [duplicate]

Let's consider two tables given by T1 = Table[{i,j,f1[i,j]},{i,0,2},{j,0,3}]; T2 = Table[{i,j,f2[i,j]},{i,0,2},{j,0,3}]; The functions ...
4
votes
2answers
293 views

What is the efficient way to code Successive Over-relaxation (SOR) method in Mathematica?

I have written a SOR method (SOR is this method) code using C-style procedural loops. However, I think there might be (much) better ways to achieve the same end in Mma avoiding these loops. So my ...
4
votes
1answer
234 views

Apply color function to matrix plot

I want to apply the following color rules to a large table of numbers. I have extracted a part of the table to use as an example. I would like to assign 5 different colors to 5 different ranges of ...
1
vote
1answer
75 views

Simple subtraction question [duplicate]

I have two lists. a = {{2, 2}, {3, 3}, {4, 4}, {5, 5}}; b = {1, 1}; I want to subtract a from ...
2
votes
2answers
65 views

Ordered indices of a multiple product or sum

Given a summation like $$\sum_{1 \leq i_1 < i_2 < \dotsc < i_k \leq n} f(i_1, i_2, \dotsc , i_k)$$ how can the lists of indices be enumerated? For example, if $n=4$ then the possible lists ...
2
votes
0answers
49 views

What is “ (Dialog) Input [ ] := ” after evaluating a cell?

I have done a time-consuming run and calculation. After many hours ( about 7 hours!), the black color which shows that the cell is evaluating, turn into gray and a strange text appears like this : ...
1
vote
2answers
138 views

How can I create a list containing the normalized element-by-element product of two given lists?

I have to calculate: How can I create such a sum? Do I have to set the factors of each term manually (one by one), like G1 = 1, H1 = 1, G2 2, H2 = ....? ...
0
votes
2answers
83 views

How to generate a list with a loop, and put it into a variable?

I am pretty new to Mathematica and to coding in general. I want to do a very specific thing, but I unable to do it. Please explain in detail how I can make this work. Here's the details on what I am ...
10
votes
2answers
303 views

Select cases from a list

I have a list in the form : {1,1,1,0,-1,-1,1,1,1,0,0,0,0,-1,-1} No I'm trying to select only those sequences which start with 1 have a zero (or many zeros) ...
2
votes
2answers
202 views

How to select the first “lowest” (first valley) number in a list?

I would to select the first valley of the list of coordinates below. It should be {3, 1}. ...
0
votes
1answer
75 views

Matrix Operation

I have a $3\times3$ matrix A, and a function sTrans that outputs two $3\times3$ matrices in a list when given a $3\times3$ ...
8
votes
0answers
133 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 ...
0
votes
1answer
54 views

How to test if any set of pairs contains elements of other list? no matter order of elements

I want to detect if a set of pairs, for example a={{2,5},{6,3},{1,4},{8,7}} contains a given pair, for example tabu={{4,1},{2,6}} but don´t be relevant the order inside pair (pair {i,j} is equal to ...
0
votes
0answers
27 views

How to switch elements i,j in a list? [duplicate]

Are there any direct function to switch elements i,j in any list? or is necessary to create one with Do / If ? (I don´t ask for making me this function if it doesn´t exists) My target is can ...
0
votes
0answers
21 views

How do I plus these values in a list [duplicate]

Hi I need to plus 3 values together each time for the rest of the list. How do I basically add the 3 sets of values together each time. When I try Plus[] it returns the same input values back to me ...
22
votes
3answers
490 views

Undocumented form for Extract

Prompted by a comments conversation here, here's an interesting (and often performance enhancing) use of Extract: ...
0
votes
0answers
108 views

A problem with functions and Infinite expression 1/0 encountering

Following code (function) makes integrals and then replace f[x] with Cos functions and calculate the definite parametric ...
0
votes
1answer
106 views

A problem with set values

The following code is just an example to clearly explain my problem. Assume that : ...
6
votes
3answers
247 views

Map structure of irregular list, Flatten then reconstruct list using structure

I'm trying to use Compile[] to improve the performance of an algorithm. The algorithm works on a set of matrices which are not of a similar shape. Unfortunately ...
0
votes
1answer
62 views

Sorting a table of vectors with weights [duplicate]

I'm trying to simplify a table, for instance {{1, {4, 2, 0}}, {4, {2, 4, 0}}, {-2, {3, 3, 0}}, {1, {3, 0, 3}}, {-3, {0, 4, 2}}} Here the first column is the ...
3
votes
5answers
170 views

Randomly selecting and reinserting a subset of elements in a list

This question is similar to my other question: How do I randomly select 'k' positions in a list and shuffle their respective elements without effecting the other elements? Imagine first a ...
1
vote
1answer
39 views

How to set the values into some variables from different lists [closed]

I have a list of Values and a list of variables. I want to set the Values into Variables. Assume the following code: ...
4
votes
1answer
134 views

How do I randomly select 'k' positions in a list and shuffle their respective elements without effecting the other elements?

Imagine I have some list: listA = {"a","b","c","d","e","f","g","h","i","j"}; I'd like to randomly select k positions in the ...
3
votes
4answers
286 views

Find the longest constant sublist

Given a list list = {1,2,2,2,2,5,1,3,2,6,6,6,6,6,6,6,6,6,6,6,10,-3}; how to find the longest constant sublist (or equivalently the element and the number of ...
2
votes
1answer
110 views

MathLink c++ passing lists of real values simple example

So this may come down to me not being a very competent programmer but I am struggling with passing list from Mathematica via MathLink that aren't of integers. The final code I am hoping to get out of ...
1
vote
1answer
213 views

Compile with array operations

When I use the function f with only the Module ...