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
146 views

Need help defining my own rounding function

First of all: I'm a beginner with Mathematica. I'd like to define a function called Rounding which does the following: if for $x = n+a, n \in \mathbb{N}, a\in ...
13
votes
3answers
944 views

What is the most efficient way to map a linked list?

In order to work with lists effectively using common recursive patterns from functional programming, it's often most convenient to worked with the "linked list" representation, that looks like this: ...
3
votes
1answer
1k views

Select row from a table by column value [duplicate]

I have the following: animals = {{dog, black, 200}, {cat, white, 100}, {moose, brown, 500}, {zebra,black,100}} If this came from a SQL table called animals, ...
2
votes
1answer
106 views

Restoring the 1-to-1 correspondence between elements in two lists, where one list is used as a guide to prune elements from the other

when we wish to use one list to select items from another using something like Pick, writing the following code, for example, causes us to lose the 1-to-1 ...
1
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2answers
158 views

MapThread with List Manupulation

I have the following three lists: ...
2
votes
2answers
796 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
224 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, ...
0
votes
1answer
323 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
96 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
118 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
523 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 : ...
4
votes
3answers
218 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
83 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
260 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
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3answers
197 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
90 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 ...
0
votes
1answer
80 views

How to simplify or improve my code (or how to Flatten inside the matrix)?

I believe that it may be simplified, but I have no ideas anymore.. I need to flatten inside each element of array. F.ex. {{1}, 128552, 6, 1} ---> {1, 128552, 6, 1} Input data (Z - requests, t - ...
5
votes
1answer
184 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
224 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
85 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
460 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
179 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
258 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 ...
15
votes
2answers
238 views

Bug with SparseArray selector in Pick

Bug introduced in version 8 or earlier and fixed in 10.0 I have created a notebook with two cells. This is the content of the first: ...
1
vote
1answer
94 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
38 views

Number precision in a list [duplicate]

I have list with elements: ...
5
votes
5answers
527 views

Joining some strings in a list of strings

So, say I have a list of strings, representing lines in a file, like so: ...
2
votes
2answers
206 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
178 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
364 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
1k 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
242 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\}, ...
5
votes
4answers
406 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
158 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
307 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
174 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
315 views

Data Table Manipulation

Suppose that I have the following ...
3
votes
2answers
689 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
137 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 ...
4
votes
4answers
586 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
3answers
112 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
830 views

Convert list to sequence

I was just thinking how Tuples was created so , I came up with this, ...
1
vote
2answers
165 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
274 views

Manipulating sparse array elements

Suppose I have two sparse arrays ...
6
votes
3answers
303 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
222 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
205 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
1k 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
215 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
61 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 ...