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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2answers
134 views

MapThread with List Manupulation

I have the following three lists: ...
2
votes
2answers
409 views

Index-based Array splitting

I have an array of arbitrary elements, say strings: testArray = {"String A", "String B", "String C", "String D", "String E"}; How can I split this into two ...
3
votes
1answer
150 views

Social Network Analysis - Get the End Points of an Edge

I want to get the end points of an Edge of a Graph. For example see the following source, ...
1
vote
1answer
115 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
122 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
2answers
56 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 ...
0
votes
1answer
109 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 ...
1
vote
2answers
481 views

Research positions of lists of varying size

I'm new to the site and I am French, so I ask your indulgence for my future mistakes in English. I would like to optimise the following code : ...
3
votes
3answers
210 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 $2$ ...
0
votes
1answer
74 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
87 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
3answers
176 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
65 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
153 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
181 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 ...
0
votes
0answers
68 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). ...
1
vote
1answer
180 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 ...
2
votes
3answers
165 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 ...
2
votes
0answers
121 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 ...
11
votes
2answers
198 views

Bug with SparseArray selector in Pick

I have created a notebook with two cells. This is the content of the first: ...
1
vote
1answer
85 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 ...
0
votes
0answers
36 views

Number precision in a list [duplicate]

I have list with elements: ...
5
votes
5answers
318 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
95 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 ...
2
votes
2answers
86 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 ...
0
votes
2answers
97 views

Apply Eigenvalues to a list of matrices

I would like to apply Eigenvalues[] to a list of matrices as in the following ...
19
votes
3answers
783 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 ...
0
votes
1answer
85 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 .. ...
2
votes
2answers
156 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\}, ...
4
votes
4answers
318 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
58 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
232 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: ...
0
votes
2answers
130 views

Summarizing SQL Tables

data = Table[SQLSelect[conn, "All", {"col1", "col2"}, SQLColumn["col1"] == n && SQLColumn["col2"] == o], {n, 1, 8}, {o, 21, 30}]; This results in ...
3
votes
3answers
220 views

Data Table Manipulation

Suppose that I have the following ...
2
votes
2answers
171 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 ...
4
votes
2answers
114 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 ...
2
votes
4answers
494 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
121 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
94 views

Function to naming columns

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

Convert list to sequence

I was just thinking how Tuples was created so , I came up with this, ...
1
vote
2answers
114 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: ...
1
vote
2answers
121 views

Manipulating sparse array elements

Suppose I have two sparse arrays ...
6
votes
3answers
187 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 ...
0
votes
2answers
90 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: ...
5
votes
2answers
175 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
271 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
130 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 ...
0
votes
0answers
57 views

Given a list of pairs, average the second elements of pairs whose first elements match [duplicate]

Say this is my list: mylist={{1,4},{1,6},{1,11},{2,12},{2,14}} I want to do an operation that looks at the first element of each pairs, and for all those that ...
1
vote
2answers
108 views

How to work with lists of functions

I have some lists of interpolated functions and I want to know if there is an easy way to operate with them. A simplified example: ...
4
votes
3answers
334 views

Finding elements from a sparse matrix

I am dealing sparse matrices of very large dimensions. I need to locate the positive and negative elements of the matrices and make lists of their corresponding positions. Of course I can write a ...