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

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0
votes
0answers
9 views

Read off entries of UndirectedEdge

Suppose I have an undirected edge e=UndirectedEdge[a,b]. How do I extract one of the entries a,b of e? I tried accessing e like a list, but that didn't work (...
5
votes
2answers
64 views

How to partition a list according to a value in the list

I have a list of the form $\{\{d_1,c_1\},\{d_2,c_2\},\ldots,\{d_n,c_n\}\}$. The values c_i take values between $1,\ldots,k$. I want to partition the data into $k$ lists according to the values $c_i$. ...
6
votes
4answers
249 views

How do I find the number of countries that have a type of industry?

I am trying to find the number of countries that have a certain type of industry. Currently, I have this code: ...
4
votes
2answers
89 views

Sorting out atom types in an XYZ file

I am trying to rewrite the output of "VertexCoordinates" such that instead of a hybrid list of atoms and coordinates that result from using the following input program, I want all coordinates of the ...
1
vote
1answer
116 views
9
votes
6answers
232 views

Is there a better way to add a “key” for the list of GatherBy?

In ruby , 1.upto(10).to_a.group_by{|x| x%3} gives {1=>[1, 4, 7, 10], 2=>[2, 5, 8], 0=>[3, 6, 9]} I would like use ...
12
votes
7answers
393 views
1
vote
1answer
220 views

Frequency of elements in a list (merging tally data) [duplicate]

I've got a list in the format of list={{a,1},{a,1},{b,1},{c,1},{b,1}} And I want it to "compress" into a list of pairs ...
3
votes
2answers
103 views

How to define even permutations correctly?

I define even permutations as following, but there may be some error. I use it in two different way and get different output. ...
3
votes
4answers
88 views

Working with calculations that depend on the previous value in a list

I'm trying to make calculations on a list that depend on the previous value. In my case I'm doing event detection - detecting the point where a value rises above some threshold for the first time ...
3
votes
4answers
147 views

One to Many Lists Merge

I have two lists: ...
4
votes
0answers
182 views

Strange behavior of undocumented RawArray and ArrayObject expressions

I discovered several strange results and inconsistencies while trying to understand what undocumented RawArray and ArrayObject ...
2
votes
1answer
49 views

Compare some lists, if elements are almost equal

I've got the solutions of three systems on two variables (a and b) that gives results sometimes almost equal. The three list are not of equal length! For example: ...
0
votes
1answer
60 views

How to sum 2 tables? [on hold]

this is what we've got: ...
3
votes
1answer
57 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.
2
votes
3answers
102 views

How to multiply specific columns in a matrix of data?

So I need to make a plot of some ~2000 data points I have from a spreadsheet. I'm able to import the data just fine, it stores it like so sundat ...
0
votes
0answers
108 views

Conceptual understanding of patterns [on hold]

Anyone who uses Mathematica's patterns cannot be left unimpressed by its power. To gain an understanding on how it might be working internally, I thought about the process and came up in fact with ...
3
votes
1answer
55 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: ...
9
votes
5answers
698 views

Coalition Games

Suppose an election produces the following result: result = {{"a", 120}, {"b", 80}, {"c", 50}, {"d", 30}}; Letters are parties and numbers seats. To form a ...
4
votes
6answers
627 views

Convert a string into a list of numbers

I got the following problem I don't know how to solve or if it's at all possible to solve(I'm quite new to Mathematica and don't have an IT background, so please explain slowly if possible:)) I'm ...
8
votes
7answers
557 views

Populate an upper triangular matrix from a vector of elements

What is the best way to populate an upper triangular (or alternatively: lower triangular or symmetric) matrix from a vector of elements? This example input: ...
8
votes
3answers
312 views
4
votes
1answer
90 views

Random symmetric matrix

Suppose first that I want to generate a matrix whose elements are i.i.d. with distribution dist. This is easy: ...
37
votes
5answers
2k views

Partitioning with varying partition size

How can I partition a list into partitions whose sizes vary? The length of the $k$'th partition is a function $f(k)$. For example: if $l = \{1, 2, 3, 4, 5, 6\}$ and $f(k) = k$. Then the partitioning ...
31
votes
6answers
2k views

How to visualize/edit a big matrix as a table?

Is it possible to visualize/edit a big matrix as a table ? I often end up exporting/copying big tables to Excel for seeing them, but I would prefer to stay in Mathematica and have a similar view as in ...
6
votes
3answers
199 views

How to count number of observations/rows within each group

I have a huge unbalanced panel data. I want to count number of rows within each group. For example, I have the following data: ...
4
votes
3answers
117 views

Combining more than two lists by first column as index

Please bear with me. It might be easy but its been hard for me. I have say three lists: ...
2
votes
2answers
41 views

Column Operation - Subtract part of nested list from part of another nested list [duplicate]

I have two lists with x- and y-coordinates with different z-coordinates of the form {{x0, y0, z0_1}, {x1, y1, z1_1}, ..., {xn, yn, zn_1}} and ...
3
votes
2answers
87 views

Sublists of Random Permutations

What is an efficient way to create a list of (psudo)randomly chosen permutations? I'm trying to create a list like below: ...
1
vote
2answers
54 views

How to append to a list of lists elegantly [duplicate]

I have have list of lists and I would like to be able to append an element to the start of each list. I am sure there must be an elegant solution. EG: a and ...
1
vote
1answer
45 views

ListLinePlot of data imported from an Excel file [duplicate]

This is a continuation of another very similar question about how to plot structured data using ListLinePlot. Here is a sample data imported from an Excel file: ...
0
votes
3answers
97 views

How to manipulate with external data?

I have a .txt file which contains a lot of triples (a, b, c) (one per row) which should be coefficients of my equation ax^2+bx+c=0. I want to include each triple in .nb file and solve each equation. ...
-2
votes
1answer
98 views

How can I produce a list of solutions for a function which is updated with updated variables using for loop?

I need to loop over a set of equations, solving for X and adding the new X value to the old X value at each step. The output I need is a list ...
7
votes
3answers
195 views

Issue with very large lists in Mathematica

I have a need to work with very large arrays of data in Mathematica. The length of the list is not known upfront. The typical size is a few hundred thousands elements and could easily go beyond a ...
6
votes
2answers
246 views

Finding the coefficient of a certain power in a generating function

I want to compute $(t^1+\dots +t^5)(t^2+\dots+ t^6)(t^3+\dots +t^9)$ and find the coefficient of $t^{15}$ for example. $t$ is an indeterminate Now in Maple this is simply as ...
0
votes
2answers
144 views

Indirect transformation based on a list of data points

I have a set of data which describes the Intensity function $Int(q)$ as a function of $q$. The data list provided below provides the shape of $Int(q)$ versus $q$.How can I use this information to ...
1
vote
1answer
106 views

Inverting matrix of unknown size

I have a matrix that has a variable number of columns and rows (but it is always square). The matrix is: $$ \Gamma = \begin{bmatrix} \Theta & 0 & 0 & 0 & T & 0 & R_j \\ ...
3
votes
1answer
70 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
2answers
79 views

Wrapping Interval Notation for Take

I'm trying to implement the solution to a math problem in Mathematica, but my code can't handle a particular boundary case. I think that I could implement a function that would do what I want it to, ...
10
votes
3answers
164 views

Pick with nested list

I have a list of pairs of values. Some of those pairs are invalid based on another list. I would like to select only the valid pairs. ...
16
votes
4answers
328 views

Make MapIndexed listable

My goal is to apply MapIndexed to every element of a nested list without destroying the arithmetic operations within the elements. For example, let's start with ...
6
votes
3answers
132 views

Mapping a function over the parts of a deeply nested Array

I have two tensors: tensorS = Array[Subscript[s, #1, #2, #3, #4] &, {2, 16, 16, 19}]; tensorR = Array[Subscript[r, #1, #2, #3] &, {2, 16, 19}]; ...
7
votes
4answers
379 views

Is there a way to riffle more than two lists?

I thought Riffle would generalize such that Riffle[{a,b,c},{1,2,3},{x,y,z}] would return ...
2
votes
2answers
77 views

How to make functions from datasets

I have a csv that encodes the results of plugging certain parameters (say, A and B) into certain functions (say, ...
2
votes
1answer
36 views

Manipulating lists with uneven amounts of entries

So I have a list like so list={{a},{b,c},{d,e,f},{g,h}} and the basic logic I want is to be able to manipulate each of the nested lists individually. So If I ...
2
votes
2answers
74 views

Componentwise Addition of TemporalData

I'm a little confused with the TemporalData structure in Mathematica, in the sense that it doesn't seem to behave like a list. What I'd like to do is plot the sum ...
5
votes
1answer
119 views

How to efficiently select element in a list of lists?

How can I write an efficient version of the following statement? Cases[list, {_, feature_} /; feature < constant]; // AbsoluteTiming List is of the form, list ...
6
votes
2answers
203 views

Is there a bug in the Part function of Mathematica 10?

I am using Mathematica 10 now. I typed code below {{1, 2}, {2, 4}, {3, 6}, {4, 8}}[[;; , 1]][[1]] and this gives result 1 ...
3
votes
3answers
150 views

Breaking up combined data into several smaller data sets

I have one combined data with first number as the x-value and the remaining as different y-axis values (y1,y2,y3...). How do I break this combined list, data= (x,y1,y2,y3...) into smaller lists, such ...
1
vote
1answer
88 views