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

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1
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1answer
100 views

How to replace a list with the result list after each iteration [closed]

I have some initial values such as L1 list: L1={10,20,30,40,50}; I want to use the L1 ...
0
votes
1answer
85 views

How to prepare (copy/paste) data from Matlab?

What is the best way to get data from Matlab to Mathematica? For a new project I want to copy/paste a table (or part of it) of datas from Matlab to Mathematica. Copyed from Matlab it is: ...
0
votes
1answer
103 views

Advice on Gather

Is there a better way to write this gather? I have a list of particles, "particlelist", and a list of particle coordinates, "coordlist" and I want to put all the particles into a 3-dimensional ng x ...
14
votes
4answers
358 views

“Unflattening” a list

Imagine we have a list with some hierarchical structure: list = {{{2,3},{2,4}},{{{3,4}}},{{5,6},{7,8}}}; Which we then flatten to some level in order to process ...
0
votes
2answers
50 views

How to obtain all the partitions in a set $A$ such that the union of these partitions equals $A$?

I'm trying to make a visual proof on the irrationality of $\sqrt{2}$. At the moment, I've created a figure to show that $b^2$ elements always constitute a square: And I want to show that it's not ...
3
votes
3answers
196 views

Finding a better way to define a matrix

I first defined a 171x171 matrix containing only zeros and then replaced 18 specific rows with nonzero entries. The other $153$ rows will be average of $2$ of the existing $18$ rows. Rows $2$ ...
16
votes
4answers
467 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 ...
0
votes
2answers
64 views

Selecting index position of data from a table that is less than a certain value

I have a table of numbers with a few thousand entries, and I'm trying to find the first index that is less than a particular value. An example of the table I'm working on is as follows: ...
0
votes
1answer
67 views

Running function - updating list - run function etc

I am making a larger program, so I would prefer to give a short example of my problem: ...
0
votes
1answer
58 views

Index of iteration inside NestList [duplicate]

I have a list of RandomReal: delta = RandomReal[{-0.01, 0.01}, 1000] I want to add each element of the list to the ...
1
vote
1answer
101 views

Format Preservation of FullSimplify on Indexed System of Autonomous Equations

I currently have a large system of 150 autonomous differential equations. I've indexed a more managable dummy system of identical form, using Part to reference ...
1
vote
3answers
163 views

How to update a list in a function in each iteration

There is a list with numbers 1 to 8 ( p1 ) and another list (j) which contains 4 numbers which shows different 4 positions of ...
2
votes
1answer
46 views

Identifying and isolating sections of overlap in a set of integer intervals

I have a very large array like the following: {{1,10},{8,9},{9,20},{34,40},{41,42},{43,50},{47,53},...}; Now, imagine that every element in the array corresponds ...
5
votes
1answer
140 views

How to combine matrix with array without cycles?

I am new to Mathematica. And I'm sorry for my English. I have created a matrix ($6 \times 4$) and an array ($1 \times 4$). I want to get another matrix that will have the first element from the array ...
1
vote
3answers
155 views

How to replace identical positions in two different lists

Assume that I have two lists like : list1={1,2,3,4,5}; list2={a,b,c,d,e}; I want to replace some elements from list1 into ...
1
vote
2answers
211 views

Thread over a nested list top to bottom until non-list elements are found

I have a nested list: list = {1, 2, {3, 4}, f[a], {2, h[b]}} I would like to apply a function g to all elements of the ...
14
votes
5answers
735 views

Picking random items out of a list only once

I'm trying to create a function that randomly returns a value from a list but remembers the values that have been given before. At the end when the list is empty it should return an empty list. ...
0
votes
0answers
61 views

Optimization of vector manipulation

I'm trying to implement an upwind scheme for solving transport equation (at first, I work with no right hand side and the simpliest case possible - velocity is constant, initial data is smooth, etc). ...
2
votes
0answers
89 views

Faster Ways to compute recursive summation

It takes a long time to compute the summation below, and I'd like to know if there are some better ways to compute things faster. I have used $3$ ways to calculate, but they are very unsatisfactory. I ...
1
vote
1answer
116 views

How to find the local maximum of a list [duplicate]

I have imported a wav sound that a = Import["sound.wav"] and we know that soundStrength = a[[1]][[1]] is a list of sound ...
10
votes
2answers
418 views

Fastest way to check for List membership

I have a set of say 100 numbers {1,3,7,11,19,...3971}. All elements are previously determined. I want to check whether ...
2
votes
2answers
142 views

list of vectors with prescribed sum

Let $a\in\mathbb{N}^n$ and $k\in\mathbb{N}\!=\!\{0,1,2,\ldots\}$. How can I efficiently generate the list $$\{(a_1,\ldots,a_k); a_1,\ldots,a_k\!\in\!\mathbb{N}^n\!\setminus\!\{0\}, ...
2
votes
3answers
155 views

Extracing information from a table

I am new to Mathematica. I have created a table of real numbers. I want to create a new table that contains the set of values of $i$ such that, in my original table, the $i$th entry is greater than ...
1
vote
1answer
80 views

Matching variables with Subscripts yielding True and False

I am trying match variables with subscripts just returning true or false depending if pattern is matched. My try is to use Cases. However the following does not ...
1
vote
3answers
297 views

How to expand the size of the matrix automatically?

I have a matrix in 2x2 a ={{x, y}, {z, u}} I want to expand this matrix 3x3 b ={{x, y, y}, {z, u, x}, {z, x, u}} 4x4 ...
11
votes
2answers
188 views

Bug with SparseArray selector in Pick

I have created a notebook with two cells. This is the content of the first: ...
0
votes
0answers
35 views
5
votes
5answers
266 views

Joining some strings in a list of strings

So, say I have a list of strings, representing lines in a file, like so: ...
0
votes
2answers
83 views

How can I select elements that are true

I have a list of lists. For example, list = {{0,1,0,1,true},{0,0,0,0,false},{0,1,1,1,true},{1,1,1,1,false},{2,2,2,2,false}} I'd like to find all lists that ...
0
votes
2answers
71 views

Apply Eigenvalues to a list of matrices

I would like to apply Eigenvalues[] to a list of matrices as in the following ...
18
votes
3answers
700 views

How to extract the edge from a set of points

I have an accumulation of points representing a body as you can see in the image below. From this data I want to generate a list of points or a curve, which is the envelope. The first idea was a ...
2
votes
2answers
66 views

adding vectors of unequal length [duplicate]

If I have hundreds of vectors of unequal length that I need to sum, what is the cleanest way to do so? So, if I have as input inp={{a,b,c,d},{e,f,g},{h}} I want ...
10
votes
4answers
323 views

How to add lists with unequal length?

Given lists of unequal lengths, I want to add them together element-wise, treating missing elements as zero. For example, {1, 2, 3} + {a, b} + {x} should give ...
0
votes
1answer
66 views

Populating an array with outputs of a function [closed]

I have searched, but didn't find much help on my issue. I have an optical physics problem that I'm working on .. ...
4
votes
2answers
101 views

Values (or positions) of array row elements within a specified number of positions from target value

I have the need to collect values from the rows of rectangular arrays of arbitrary precision integers, given a target element value and allowed "distance" (positions +/- within the row from found ...
3
votes
4answers
258 views

Efficient method for Inserting arrays into arrays

This is strongly related to the following Questions: Looking for a way to insert multiple elements into multiple positions simultaneously in a list Building matrices by attaching vectors (columns) ...
1
vote
2answers
43 views

How to switch between a binary number as String and a as a list of digits?

I was trying with String Functions and I viewing any posts and have no results I want to know 1.- From cromo33 = Table[RandomInteger[], {i, 1, 33}] cromo33 ...
3
votes
2answers
195 views

Mapping multiple functions over an array

I am looking for an elegant way to Map multiple functions over an array. My problem looks something like this: Consider a list of functions: ...
3
votes
3answers
158 views

Data Table Manipulation

Suppose that I have the following ...
1
vote
2answers
125 views

Removing trailing zeros from a list

If I have a list like list1={2334.,342.,0.,0.,2322.,0.,0.,0.,0.,,,,,,}; it's easy to remove to trailing blanks with ...
2
votes
4answers
469 views

More elegant way

I read ReplaceOrRemoveInvalidOrMissingData Mathematica documentation, and I tried to apply the same approach to my dataset. I've got two problems, but one is only a style problem! There is one more ...
0
votes
1answer
79 views

Problem ListLinePlot with 2 data sets [closed]

I am trying to plot 2 data sets with ListLinePlot and my problem is that no graph shows up. When I plot a single data set i.e. ListLinePlot[Aluminium] it looks ...
0
votes
3answers
89 views

Function to naming columns

I often import files from excel or csv files and they come in a format like this: ...
1
vote
2answers
65 views

Manipulating sparse array elements

Suppose I have two sparse arrays ...
0
votes
2answers
98 views

Factorization of a list with composite integers to a combined list of all prime factors

The following function io[aIn_] produces a list bOut containing ALL the prime factors of an Integer via the standard function FactorInteger[]. My code is: ...
2
votes
2answers
177 views

Convert list to sequence

I was just thinking how Tuples was created so , I came up with this, ...
6
votes
3answers
161 views

Enumerate the 1-factors (perfect matchings) of $K_n$

Introduction I would like to enumerate the 1-factors, or (near-)perfect matchings, of the complete graph Kn. The adjacency list representation for Kn is basically { (x, y) | 1 ≤ x < y ≤ n }. For ...
5
votes
2answers
160 views

Join lists of lists with unique id

Sorry for the vague title, but I can't describe my problem properly and shortly. I am maintaining a list of players and their games with the following form: ...
1
vote
1answer
114 views

Collecting lists using Reap/Sow

I have a list like {{a,x},{b,y},{c,x},{d,z},{e,y}} and would like to produce from it a list formed by collecting all top-level elements whose second components are ...
2
votes
1answer
116 views

Speed up Select on large list

I am running this on a very large list, it is important to notice that some times the dates in v occure several times, and I want the selected list to show the same amount. This produces the right ...