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

learn more… | top users | synonyms (3)

2
votes
3answers
75 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
204 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 ...
4
votes
8answers
400 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
204 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
125 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 ...
0
votes
0answers
48 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?
6
votes
6answers
430 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 ...
8
votes
0answers
147 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
238 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
1answer
74 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 ...
6
votes
8answers
287 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 ...
1
vote
4answers
103 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 ...
3
votes
2answers
248 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 ...
10
votes
8answers
396 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. ...
1
vote
2answers
37 views

how to extract a matrix and a vector from a vector [duplicate]

I have a vector like this: V = {a*exp1+b*exp2+c*exp3, a*exp4+b*exp5+c*exp6, a*exp7+b*exp8+c*exp9} and I want to get : ...
2
votes
0answers
134 views

Convex optimization

I am playing with some Compressed Sensing (think single pixel camera) applications and would like to have a Mathematica equivalent of a Matlab package call Convex Optimization (CVX). Specifically, I ...
4
votes
2answers
111 views

Faster Alternative to DeleteDuplicates for deleting elements in list [duplicate]

I have a list in this style data={{a1,b1,c1,d1,e1,f1}, {a2,b2,c2,d2,e2,f2}} I need to delete all elements in which b1 is ...
11
votes
12answers
565 views

How to group each element with each consecutive elements in one head

Suppose I have the following list: list = {a, b, c, d} I want to generate this result: ...
-2
votes
4answers
206 views

Compare elements in a list

Assume that there are three different points in x-y coordinate like: p1={4, -1}; p2={5, -2}; p3={1, 5}; In order to compare these points to each other in a ...
6
votes
2answers
270 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 : ...
11
votes
2answers
322 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
4answers
173 views

Need an efficient way to do this list manipulation

Lets say i have two lists with me as given below: l1 = {4, 6, 8, 9, 10, 12}; l2 = {2, 3, 4, 5, 6, 7}; Now i have a function S2P(details irrelevant) which takes ...
1
vote
4answers
143 views

Minimum and maximum values under conditions

Let's create some sample data ...
3
votes
5answers
137 views

Creating a new list by dropping sub elements of the original list

Suppose I have a nested listed as follows, {{{1,2},{3,4,5},{2,3}},{{2,3,4},{5,4,1},{1,4,3}},{{3,4,5},{3,4,5}}} Where the elements are, ...
2
votes
3answers
142 views

Using select to pick out elements of nested lists in an odd way

Suppose I have a nested list such as, {{{A, B}, {A, D}}, {{C, D}, {A, A}, {H, A}}, {{A, H}}} Where the elements of interest are, ...
8
votes
0answers
233 views

Learning Resources for Data Science in the Wolfram Language

I'm delivering an upcoming course on Data Science with the programming/analysis done predominantly in the Wolfram Language. I created the following table to leverage students' familiarity with Lists ...
0
votes
0answers
121 views

Improving the speed of evaluating Table with nested functions

I am a Mathematica novice working with a stack of 1024 x 1024 WatershedComponents (or MorphologicalComponents) label matrices ...
8
votes
4answers
320 views

Fast method to select matrix elements based on a vector of positions

There is an operation for which I have long wanted to find a better solution. Let: a be a matrix of dimensions $m\times n$ ...
3
votes
3answers
174 views

Zero-order interpolation not going fully around

Connected to this question, I want to do a zero-order interpolation of a bunch of datapoints which is periodic. The code I use is as follows: ...
8
votes
1answer
209 views

How to slice TimeSeries data?

When retrieving curated data, v10 now returns TimeSeries objects. For example, ...
2
votes
3answers
279 views

Create a list of random reals

How can I create a list of random pairs $(x,y)$ where $0<y<x<1$ and $x,y \in \mathbb{R}$ ? I can't seem to place that inequality restriction on the random numbers that are generated.
1
vote
4answers
116 views

Replacing more than one element from a Sublist

The following expression allows me to extract the value of x and y: ...
0
votes
2answers
47 views

Defining a function from a list [closed]

I have a list of 49 numbers, and I would like to define a function f such that f(n) is simply the nth number in the list. How can I do this?
8
votes
7answers
632 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: ...
0
votes
1answer
47 views

Help with programming(using list) [closed]

I would like to make a program which gives me what is the greater natural number "n" less than an arbitrary given natural number "k" which satisfy: for each prime divisor "p" of n, p^2-1 divides n. I ...
3
votes
5answers
201 views

Take the next element in a nested list

My problem is the following: Consider a list of elements. To better understanding my following explanations, I would take this example: ...
1
vote
1answer
103 views

Setting a Row from a Matrix as Variable

I'm not advanced in Mathematica but I'm trying to get better. I have a big set of Data and I want to Plot the first row against ...
1
vote
1answer
117 views
2
votes
1answer
75 views

What is the correct way to plot a dynamically generated list of functions?

For example, I want to generate a list of random waves and plot them. Then I wrote f:=Random[Real] h:=Floor[f*20] And then ...
1
vote
3answers
48 views

Collect the lists

I have a list of lists from which I pick out the positions of the number 1 and then print out these positions for each list. I am having some trouble collecting what I am printing into a list / matrix ...
2
votes
2answers
141 views
2
votes
2answers
122 views

Map 2 list to a function

Im playing around with CountryData and I want to pass it 2 lists as argument, listCountries = {...} and ...
4
votes
3answers
140 views

Symmetric list with maximum in center

How to sort a list, e.g. RandomInteger[{0, 100}, 50] that the Maximum is in the center and all other elements are placed symetrically in descending order around ...
2
votes
2answers
173 views

Binarizing a matrix

I have an image with a few bright pixels with the remaining ones very dark. The difference is in orders of magnitude. I want to binarize this matrix (corresponding to the image) making all values ...
2
votes
3answers
126 views

Speeding Up Replacing of Labels in Large Matrix?

I am Mathematica novice and am trying to find a fast way to replace labels in some rather large matrices (512x512 or 1024x1024) that have resulted from segmenting images with WatershedComponents or ...
19
votes
3answers
669 views

DeleteDuplicatesBy is not performing as I'd hoped. Am I missing something?

Déjà vu: a new-in-v10 function should provide a better solution to an old problem, but my enthusiasm is curbed when I run timings. This time the function is ...
0
votes
1answer
32 views

Interactively Manipulate SparseArrays or Lists

I'd love to use SparseArrayor List to group a set of parameters together in a function. ...
1
vote
1answer
58 views

Integers in Range have trailing decimal - how to remove?

I want to create a list like {0,0.2x,0.4x,0.6x,0.8x,1} If I try Range[0, 1, 0.2] x what I get is ...
2
votes
3answers
172 views

What is the order of faces on a D20? How can I optimize the order of faces on a D-n?

I am creating a customizable D20 for 3D printing using OpenSCAD, with the following code: ...