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

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3
votes
1answer
183 views

How to efficiently take complement of two big lists?

I have a giant list l1 and some smaller lists l21, l21, ..., ...
3
votes
1answer
237 views

How to partition MatrixPlot graphics?

Is there an easy approach - hopefully built-in - to partitioning MatrixPlot graphics into rows or columns (or both) of graphics sharing the same underlying options? ...
3
votes
1answer
286 views

n-fold symbolic integral in Mathematica

I am trying to compute symbolically a n-fold integral (n is a parameter of a function) over, say, the cube [0,a]^n. My code looks like this ...
3
votes
1answer
87 views

Creating an autokey cipher function

Can someone help me with putting what I can say in words into code. I want to create autokey encrypt and decrypt functions (just wanting help encrypting and then can figure out decrypting). Everything ...
3
votes
4answers
102 views
3
votes
3answers
177 views

Trouble with Position[]

I am in trouble with Position, Although my example works as expected it throws a warning. Position[{{a,b},{a,c},{a,b}}, _?(#[[2]]==b&), {1}] During ...
3
votes
1answer
147 views

Making a list of rules from the list of elements

Starting from the list: {f[q1, q2], f[q3, q4], g[q1], g[q2, q3, q4], d[k1 - q1], d[k2 - q2 - q3 -q4]} I would like to get the result: ...
3
votes
1answer
65 views

How can I create a set (list) provide a kind of rule/algorithm?

Example: S = {r ∈ Q : r² < 2} Let S be the set of all rational numbers whose squares are less than 2. It follows that 1 ∈ S, 4/3 ∈ S, but 3/2 doesn't ∈ S because 9/4 ≥ 2. Thank you.
3
votes
1answer
98 views

How to efficiently select elements from a Hash?

How can I write an efficient version of the following selection statement: Keys[Select[hash, # < constant &]]; // AbsoluteTiming hash can be made from: ...
3
votes
1answer
66 views

Part specification error only in LogPlot

I've a problem. I defined a simple list and a function like below: lst := {5, 10, 20} f[m_] := lst[[Floor[m/10]]]; and drew a plot ...
3
votes
2answers
109 views

How to modify the elements of a list in a loop?

I have a list with points coordinates. And I'm trying to traverse it and perform some matrix operations on each point. But I have a problem with storing modified points in the initial list instead of ...
3
votes
3answers
275 views

Data Table Manipulation

Suppose that I have the following ...
3
votes
1answer
120 views

How do I get the length of held list without evaluating the list?

I used Extract with Hold to retrieve a sublist containing expressions I didn't want evaluating, e.g. ...
3
votes
1answer
107 views

Recursion when randomizing elements in a list

I want to randomize certain elements of a list; Since the code list = {a, b, c, d, e, f, g}; list[[{1, 3, 5}]] = RandomSample@list[[{1, 3, 5}]]; list works fine, ...
3
votes
2answers
215 views

How to delete all rows in datafile that contain a string

I'm importing some data from a file. However, the file was created by an unreliable instrument, such that the data looks like this: ...
3
votes
1answer
184 views

Levels and slots

I am struggling with levels and #, if I understand this I think I will be able to grasp the entire concept. ...
3
votes
2answers
102 views

Linear interpolation of a list between periodic anchorpoints

I have a list of the form: list = {1,1,1,2,2,2,3,3,3,4,4,4,7,7,7,19,19,19}; Where we can see that there are an ordered set of integer values that repeat ...
3
votes
1answer
531 views

A rotation-like transform on a matrix

Do not be confused with comments, those are for previous version of the question - Kuba Imagine I have a matrix of the form: ...
3
votes
1answer
139 views
3
votes
1answer
131 views

Filtering the elements of an array to split them into two categories

So, I am new to Mathematica, and I am trying to write something that involves taking values from one array and separating them into two different arrays. My code for doing this is: ...
3
votes
1answer
265 views

Replace elements in a list

Suppose that I have a list: ...
3
votes
2answers
94 views

How to generate a list from an iterator and some arbitrary function

Suppose I'd like to generate a table of integers: Table[i, {i, 10}] Great; now suppose I want only the integers that are even ...
3
votes
1answer
293 views

Operations on a List of Vectors (Norm)

I have a List containing vectors. The coordinates are random numbers: r = {RandomReal[{-1, 1}, n], RandomReal[{-1, 1}, n], RandomReal[{-1, 1}, n]}; Now I want to ...
3
votes
3answers
80 views

Generating increasingly longer lists from a single list

I start with an array such as {{1,1},{0,1},{-1,1}}. (1) I want to create an array from this which replaces each array inside the array with 3 new arrays, one ...
3
votes
1answer
76 views

Remove values from list element, and add to other element

Basically what I need is to make a list of 400 elements, all have value 1. The next step is to create a function, that subtracts value (-1) from an element, and adds that to another element. So: ...
3
votes
1answer
117 views

Read and write files

I have a text file, its content is(for example): ...
3
votes
2answers
108 views

Find Lists with intersecting sublists

I have a list of the following form: ...
3
votes
1answer
684 views

Plotting multiple lists of complex numbers

The user #Nasser showed an elegant way to plot complex numbers: ...
3
votes
1answer
460 views

Exporting/Importing a Table of complex numbers

I'm generating a long table of list of the form: PN={{1,2,1+i},{3.5,2.6,2}...},{...},... Using: Export["PN.dat", PN, "Table"] ...
3
votes
2answers
616 views

Dynamically remove element from list based on test

Suppose I have a list l = {a, b, c, d, e, f....} I would like to remove one of each pair {x,y} if some function ...
3
votes
2answers
176 views

Modify all the second elements of every pair in a list of pairs

I have a list in the form {{a, 1}, {b, 2}, {c, 3}}. Let's say I want to operate a transformation on all the second elements of each sublist, but this transformation is a function of them all ...
3
votes
1answer
212 views

Indexing of Large Autonomous System of Equations for Use in NDSolve

I currently have a list of ~150 autonomous ODE's that I need to be able to work with using NDSolve. Fortunately I already have them formatted in plaintext, which ...
3
votes
1answer
204 views

Efficiently finding the maximum value of a column in a matrix

Imagine I have a matrix of the following form: TestArray = $((a_1,b_1,...),(a_2,b_2,...),(a_3,b_3,...),...)$, where a specific example might be: TestArray = ...
3
votes
1answer
60 views

Output function control and manipulation for efficient computation

I have taken note of a similar post related to modifying function parameters. I tried to adapt Kuba's solution to this post but I can't get it to work. I will illustrate my problem using a similar ...
3
votes
0answers
80 views

Why does Part behave like it transposes lists? [closed]

From the documentation of Part: Part[expr,i,j,...] is equivalent to expr[[i]][[j]]... ...
3
votes
0answers
295 views

Taking real and imaginary parts of indexed functions and speeding up ComplexExpand

I am setting up a large system of ODEs and in order to use the IDA method (which is sig. faster for my system and thus attractive), I must split my equations into real and imaginary parts. I am ...
3
votes
0answers
98 views

Gather dependency on list order?

I get intrigued about Gather behavior on this post. I thought that Gather was invariant under list order? Here is the result I ...
3
votes
0answers
67 views

Listing all combinations produced by picking one element from each of several sets [duplicate]

I have a problem like this, I am given the following sets {a,b,c}, {d,e,f}, {h,i,j}. I want to pick one element from each set, and output a list of all the ...
3
votes
0answers
150 views

List manipulation, replace a value [duplicate]

I have the following list: ...
3
votes
0answers
193 views

Exporting Specific Cells of Many Workbooks into One using Mathematica

I currently have a large number of detailed files from which I would like to extract certain cells' information to make an Archive spreadsheet. There are approximately 9 parameters of each ...
2
votes
6answers
1k views

Selecting elements from a list one by one

I have an list: l = {{4,5},{7,8},{9,5},{3,2},{1,2},{13,12}}. I want to take the elements in the list in the sequential order. For example the first element in ...
2
votes
3answers
281 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.
2
votes
3answers
637 views

Problem with Union and Intersection

Consider the following: list={{a,b,c},{c,d,e},{d,e,f},...{x_,y_,z_}}; I would like to apply Union on the elements of the list ...
2
votes
3answers
253 views

Picking items from a list

There's probably a Mathematica primitive to do this, but I don't know what it is...suppose I wanted to construct a list of all integers from $1$ to $n$ that were not divisible by $12$, and that were ...
2
votes
5answers
221 views

Treat list as cyclic

I am considering the following case. Say that T={p1,p2,p3} represents a triangle. In addition, I want to parameterize the edges of the triangle ...
2
votes
4answers
225 views

Get 'new' list of data by manipulation 'old' list

Assume I have the the following list of data: valuesOld = {5, 10, 15, 20, 25, 35, 40, 45, 55, 65, 80}; I would like to construct the following list: ...
2
votes
4answers
385 views

Building a list recursive with one or more arguments

Consider the following: data={a,b,c,d}; res={{a,b,c,d},{b,c,d,e},{c,d,e,f},{d,e,f,g}}; The idea is to define a function ...
2
votes
4answers
113 views

Obtaining EditDistance[] from a List of Strings

Consider the following question. I have a long selection of files (some 5,000), arranged linearly, and I want to view to what degree the files have changed between each other. For a small example, ...
2
votes
6answers
217 views

Manipulating List

I have a list: b={{1, 1}, {2, 2}, {3, 3}, {5, 5}, {6, 6}, {8, 8}, {10, 10}} I want to insert the elements in this list: ...
2
votes
4answers
224 views

How to improve the quality of the ListPlot output

I need to plot massive data stored in external ASCII files. Below is the Mathematica code I use for this job: ...