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

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3
votes
4answers
410 views

Find the longest constant sublist

Given a list list = {1,2,2,2,2,5,1,3,2,6,6,6,6,6,6,6,6,6,6,6,10,-3}; how to find the longest constant sublist (or equivalently the element and the number of ...
2
votes
1answer
275 views

MathLink c++ passing lists of real values simple example

So this may come down to me not being a very competent programmer but I am struggling with passing list from Mathematica via MathLink that aren't of integers. The final code I am hoping to get out of ...
1
vote
1answer
371 views

Compile with array operations

When I use the function f with only the Module ...
4
votes
1answer
136 views

Sectional averages of a list

I am working in Mathematica. I have a table of 200 elements. I want to calculate the mean value for the first 20 elements, for the second 20 elements and so on, up to 200. I will get a table (matrix) ...
1
vote
1answer
327 views

Generating a random sample of elements from a list that includes a subset of the list

Imagine I have a list: tList = {item1,item2,item3,item4,item5,item6,...}, and I'd like to take a random sample of numItems ...
5
votes
4answers
318 views
2
votes
1answer
142 views

Convert frequency counts to long notation in Mathematica

I have a series of frequencies of values, e.g. 5 times 1, 10 times 2 and 5 times 3, as in list={{1,5},{2,10},{3,5}} and I would like to convert this to long ...
0
votes
2answers
146 views

How to partition three years of data into daily samples

I'm trying to find mean of temperature data list. The temperature data list has 3 hours steps which means I have 365*8=2920 temperature measurements per year. My data are temperatures of 13 years. ...
0
votes
1answer
93 views

Creating If statements programmatically [duplicate]

I want to write an algorithm that returns a sequence of numbers, starting from a specified point but stopping once a criterion has been reached. For example ...
3
votes
1answer
839 views

Converting truth tables to boolean expressions

I have a truth table for a Boolean expression represented like this ...
0
votes
1answer
71 views

how to use Manipulate changing the values of a List?

How can I "change" the values in the list h={2,4,6} using Manipulate? (Next line was edited after hte first Alexi´s comment) I WANT to choose real values in h[[1]], h[[3]] , h[[3]] between 0 and 8. ...
0
votes
3answers
607 views

How to solve correctly inside a DO loop and then plot

Here is the corresponding code First the equations setup ...
4
votes
5answers
298 views

Summarize a list of pairs / (Using GatherBy and Tally?)

Given a list of (frencuently repeated and unsorted) pairs {Mode, SubMode} I want to form the list ...
1
vote
3answers
105 views

Creating Graph with two or more values in second column

For a social network analysis I have two columns. The second column has one, two or more values. Something like this: ...
2
votes
1answer
119 views

Using Total on a list supplied by a rule

I'm confused as to why Total complains about a nonatomic expression here: ...
1
vote
1answer
577 views

Selecting items in a list based on multiple tests

I have an array of strings that look like this: ...
3
votes
3answers
175 views

Wrapping a data selection in Mathematica

I was wondering what would be the most efficient way to add brackets to given elements in my data set in order to change it's form from {{a,b},{c,d}} to {{{a},b},{{c},d}}. I took a look through a few ...
3
votes
1answer
7k views

Finding the position in a list where the maximum or minimum value occurs [duplicate]

We can use Max[exampleList] or Min[exampleList] to find the maxima and minima of ...
1
vote
1answer
156 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
1k 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
111 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
vote
2answers
161 views

MapThread with List Manupulation

I have the following three lists: ...
3
votes
2answers
839 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
237 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
350 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
103 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
121 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
527 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
219 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
286 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
204 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
187 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
228 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
88 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
492 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
274 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
250 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
601 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
237 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
196 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
454 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
268 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\}, ...