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

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3
votes
1answer
27 views

Part specification error only in LogPlot

I've a problem. I defined a simple list and a function like below: lst := {5, 10, 20} f[m_] := lst[[Floor[m/10]]]; and drew a plot ...
4
votes
3answers
135 views

How to test if all the elements in a list are Integers? [closed]

Consider a list such as s={1,2,3,3,5,6,3} With IntegerQ[number] , you know if number is an ...
5
votes
2answers
64 views

Return value of Reap when using tags

I've noticed a behaviour of Reap that I don't quite understand yet. Suppose I want to Sow several values during a computation. ...
11
votes
4answers
199 views

Make MapIndexed listable

My goal is to apply MapIndexed to every element of a nested list without destroying the arithmetic operations within the elements. For example, let's start with ...
1
vote
2answers
607 views

Computing 10-dimensional volume of a 9-sphere [on hold]

I'm trying to compute 10-dimensional volume of a 9-sphere with radius r using Monte Carlo. ...
1
vote
1answer
88 views
2
votes
2answers
136 views

How to get the current index during a Scan iteration?

Is there a special keyword to get the current index in Scan ? For example, let say I have the following code : ...
6
votes
2answers
181 views

Converting a string into a nested list of strings

The following string can be converted easily into a list with ToExpression ...
3
votes
2answers
304 views

How to plot several functions without jumping? (multiple eigenvalues of a system as functions of 2 parameters)

I've been working on this research problem for months with some success by no global/proper solution to the problem. So I have square, Hermitian matrices of various sizes ($8,20,38$ dimensions) with ...
0
votes
1answer
96 views

How to create an array of functions [on hold]

For a project I'm working on, I need to solve a differential equation numerically. I know this is easily done with NDSolve, but I want to solve it several times ...
3
votes
2answers
95 views

How to modify the elements of a list in a loop?

I have a list with points coordinates. And I'm trying to traverse it and perform some matrix operations on each point. But I have a problem with storing modified points in the initial list instead of ...
5
votes
5answers
279 views

How to display operations on list elements

When applying some arithmetic operation on two lists, I'd like to display the actual operations between the elements of each list. For example, {1, 1} + {1, -1} ...
7
votes
2answers
1k views

Get the coordinates from ContourPlot and RegionPlot

How do I get the coordinates from a contour plot I've done in Mathematica? For example, I have a two-variable function f[x, y], for which I can make a contour plot: ...
2
votes
1answer
75 views

How to build a list of constraints for NMinimize

Let's say I have aset = {-1, 0, 2}. I would like to create a variable Var that takes values from that set, i.e. ...
0
votes
0answers
34 views

Plotting a List [closed]

I can't find a solution to my problem on here nor google. I'm plotting a list using ListLinePlot from a list I generated using Table. For this table, my values range as follows ...
1
vote
3answers
118 views

How to ReplaceAll independent of depth?

I have a big list which in principle can be described as this more compact list : ...
0
votes
1answer
109 views

How to plot data points in the form X, Y, E(X, Y) where X and Y coordinates are not ordered?

I have got a file with field values (RF simulation of a resonator) which consists of 3 columns: X and Y cartesian coordinates ...
5
votes
1answer
135 views

How to split a Dataset into training and testing for machine learning?

Suppose I have iris data In the Dataset Format. How to split the iris data Into training and testing for Machine learning? For example,Transform the data for Classify.
4
votes
5answers
518 views

Convert a string into a list of numbers

I got the following problem I don't know how to solve or if it's at all possible to solve(I'm quite new to Mathematica and don't have an IT background, so please explain slowly if possible:)) I'm ...
1
vote
1answer
53 views

Remove curly brackets _completely_ to map a function to the elements of a list [duplicate]

Most list manipulations can be done with Flatten, Partition and Take. I didn't managed to ...
2
votes
4answers
101 views

Import xls data with dates

I have an excel table that have 2 columns, the first one are dates, and the second one are values. I want to plot the value vs the date. I need to: first clean all the non numbers strings like ...
6
votes
3answers
241 views

Rotate lines around their midpoint

I am trying to rotate a series of lines by the same angle around their centre point. Say each line is defined by a co-ordinate at each end, simplified example below of a typical dataset. ...
1
vote
1answer
72 views

How can I write a function which takes another function of a variable and the variable itself as arguments and gives a list of critical points?

This is an exercise from Power Programming with Mathematica by Wagner. I need a function which takes a function and a variable as arguments, like this: critpts[f_,x_]:= and then on the rhs I've got ...
6
votes
8answers
229 views

Merging lists and adding common elements [duplicate]

I have two 2D arrays where some of the x-values are identical, L={{1,1},{2,2},{3,3}}; J={{0,1},{2,2},{4,4}}; I want to add these lists in the following way ...
6
votes
2answers
135 views

Problem when defining function through NIntegrate and NDSolve and Interpolation - Bug?

More than a single question, I have some doubts about the output of certain functions when defined through the result of other calculations. I am an active user of Mathematica, but maybe I haven't ...
3
votes
1answer
98 views

Read and write files

I have a text file, its content is(for example): ...
10
votes
2answers
270 views

Solving the magic backyard puzzle with MMA

I was trying to solve this puzzle using mma It looks like the generalization of the magic square. Anyway here my attempt:- There are four columns $(x,y,z,w)$ and nine rowa which are denoted by the ...
1
vote
1answer
82 views

Inverting matrix of unknown size

I have a matrix that has a variable number of columns and rows (but it is always square). The matrix is: $$ \Gamma = \begin{bmatrix} \Theta & 0 & 0 & 0 & T & 0 & R_j \\ ...
1
vote
3answers
108 views

Removing some data and replacing them with new ones

I have a data list where the elements have the form (time, velocity ). I need to remove some malformed elements in places where the data does not change smoothly and then replace those points by ...
4
votes
3answers
150 views

unlisting a nested list

I have a list like this: list = {{a,{1,2,3}},{b,{1,2,4}},{c,{{1,4,5,5},{6,3,2,1}}}} This is a nested list which each element has a name. I want to export it to ...
3
votes
4answers
168 views

Replace all symbols in a matrix with their numbered forms

I have a matrix made mostly from "x" with a few 0's thrown in: ...
1
vote
2answers
114 views

Replace a value in a nested array

When I run the following, ...
2
votes
3answers
63 views

Take a list with the amounts of the random samples from another list while holding the index

I have a list called cant with some amounts of samples to take from the list community as follows: ...
3
votes
5answers
191 views

First pair out of order

I would like to know how to efficiently determine the first pair of elements in a list that are not in order according to some predicate p. That is, list[i] > list[j] according to p, and i is the ...
0
votes
2answers
135 views
4
votes
8answers
373 views

How to sort my list?

For example I have two lists of such structure L1 = {{"Australia",a1}, {"USA",a2}, {"Norway",a3},...} L2 = {{"Russia",b1}, {"Norway",b2}, {"Japan",b3},...} I ...
3
votes
7answers
195 views

List creation/manipulation

I'd like to a create a list from A = {{a}, {b}, {c}} by taking each elements n times in the following form: ...
1
vote
4answers
95 views

Check if a scalar falls within the range given by sub-arrays of a matrix

I have a rank 3 matrix: r = {{{1, 10}, {19, 71}, {111, 159}}, {{1, 5}, {25, 63}, {118, 132}, {164, 185}}, {{1, 19}, {28, 49}, {157, 203}}}; and each of the ...
18
votes
4answers
596 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 ...
6
votes
6answers
391 views

Convert a list of rules into 2 lists of integers

If I have a list of n number of rules, what is a concise way of breaking the data into 2 lists of the first and second part of the rule? This works, but seems like an unnecessary amount of code to ...
6
votes
1answer
401 views

Finding all length-n words on an alphabet that have a specified number of each letter

For example, I might want to generate all length n=6 words on the alphabet {A, B, C} that have one ...
0
votes
0answers
46 views

Generate all strings of fixed length from an alphabet [duplicate]

I am trying to create all possible strings of length $8$ from the alphabet $\{+1,-1\}$. I am trying to get help from this question. But not sure where to start from. Any help?
7
votes
0answers
84 views

How to merge Datasets representing matrices with named rows/columns?

I am working with square (non-symmetric) matrices with named rows and columns. The data I receive is sometimes messy and rows/columns may come in various permutations. I usually need to ...
3
votes
3answers
220 views

How can I change a list to a sequence without destroying nested list

I defined a function f like f[x___, y_] := something; and if xs and ...
0
votes
4answers
95 views

Converting format of list

I have a 2D array, data = {{0,1}, {1,2}, {2,3}}; I would like to convert it such that I get the x- and y-values separately, specifically ...
10
votes
8answers
324 views

Forming an upper triangular matrix from the elements of a list

I asked this question before, but i was closed because it the question was not comprehensible enough. So i reworded it, hope that's ok. I have a list with 6 elements. ...
0
votes
1answer
43 views

Map Elements of a list to be Index of matrix

I have a sublist from Tuples[{1, 2, 3}, 2], say for example L={{1,2},{2,1},{2,2}}, and a 3 x 3 matrix ...
3
votes
2answers
216 views

Weird behavior when changing parts of matrix

I have this matrix: mat = {{1, 2, 3, 4, 5}, {6, 7, 8, 9, 10}, {11, 12, 13, 14, 15}, {16, 17, 18, 19, 20}, {21, 22, 23, 24, 25}}; and here are its second row ...
5
votes
5answers
431 views

Populate an upper triangular matrix from a vector of elements

What is the best way to populate an upper triangular (or alternatively: lower triangular or symmetric) matrix from a vector of elements? This example input: ...
6
votes
2answers
246 views

Apply function to every element of list regardless of depth

I want to apply a function to every element of a list without taking braces into account (depth level), but with the same form of output. Here is an example : ...