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

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6
votes
2answers
238 views

Faster Alternative to DeleteDuplicates for deleting elements in list [duplicate]

I have a list in this style data={{a1,b1,c1,d1,e1,f1}, {a2,b2,c2,d2,e2,f2}} I need to delete all elements in which b1 is ...
12
votes
12answers
646 views

How to group each element with each consecutive elements in one head

Suppose I have the following list: list = {a, b, c, d} I want to generate this result: ...
-2
votes
4answers
657 views

Compare elements in a list

Assume that there are three different points in x-y coordinate like: p1={4, -1}; p2={5, -2}; p3={1, 5}; In order to compare these points to each other in a ...
6
votes
2answers
524 views

Apply function to every element of list regardless of depth

I want to apply a function to every element of a list without taking braces into account (depth level), but with the same form of output. Here is an example : ...
15
votes
3answers
535 views

Solving the magic backyard puzzle with MMA

I was trying to solve this puzzle using mma It looks like the generalization of the magic square. Anyway here my attempt:- There are four columns $(x,y,z,w)$ and nine rowa which are denoted by the ...
1
vote
4answers
186 views

Need an efficient way to do this list manipulation

Lets say i have two lists with me as given below: l1 = {4, 6, 8, 9, 10, 12}; l2 = {2, 3, 4, 5, 6, 7}; Now i have a function S2P(details irrelevant) which takes ...
1
vote
4answers
191 views

Minimum and maximum values under conditions

Let's create some sample data ...
3
votes
5answers
165 views

Creating a new list by dropping sub elements of the original list

Suppose I have a nested listed as follows, {{{1,2},{3,4,5},{2,3}},{{2,3,4},{5,4,1},{1,4,3}},{{3,4,5},{3,4,5}}} Where the elements are, ...
2
votes
3answers
534 views

Using select to pick out elements of nested lists in an odd way

Suppose I have a nested list such as, {{{A, B}, {A, D}}, {{C, D}, {A, A}, {H, A}}, {{A, H}}} Where the elements of interest are, ...
8
votes
1answer
293 views

Key->Value or Value when returning (multiple) parts of an Association

There seems to be an idiom whereby multiple parts generates Key->Value forms whereas for single part specifications, only a Value is returned. This however, can lead to inconsistencies as follows: <...
14
votes
0answers
448 views

Learning Resources for Data Science in the Wolfram Language

I'm delivering an upcoming course on Data Science with the programming/analysis done predominantly in the Wolfram Language. I created the following table to leverage students' familiarity with Lists ...
0
votes
0answers
192 views

Improving the speed of evaluating Table with nested functions

I am a Mathematica novice working with a stack of 1024 x 1024 WatershedComponents (or MorphologicalComponents) label matrices ...
8
votes
4answers
658 views

Fast method to select matrix elements based on a vector of positions

There is an operation for which I have long wanted to find a better solution. Let: a be a matrix of dimensions $m\times n$ v...
3
votes
3answers
239 views

Zero-order interpolation not going fully around

Connected to this question, I want to do a zero-order interpolation of a bunch of datapoints which is periodic. The code I use is as follows: ...
9
votes
1answer
469 views

How to slice TimeSeries data?

When retrieving curated data, v10 now returns TimeSeries objects. For example, ...
2
votes
3answers
316 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.
1
vote
4answers
170 views

Replacing more than one element from a Sublist

The following expression allows me to extract the value of x and y: ...
8
votes
7answers
1k 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: ...
3
votes
5answers
263 views

Take the next element in a nested list

My problem is the following: Consider a list of elements. To better understanding my following explanations, I would take this example: ...
2
votes
1answer
113 views

Setting a Row from a Matrix as Variable

I'm not advanced in Mathematica but I'm trying to get better. I have a big set of Data and I want to Plot the first row against ...
1
vote
1answer
145 views
2
votes
1answer
121 views

What is the correct way to plot a dynamically generated list of functions?

For example, I want to generate a list of random waves and plot them. Then I wrote f:=Random[Real] h:=Floor[f*20] And then ...
1
vote
3answers
70 views

Collect the lists

I have a list of lists from which I pick out the positions of the number 1 and then print out these positions for each list. I am having some trouble collecting what I am printing into a list / matrix ...
2
votes
2answers
289 views
2
votes
2answers
161 views

Map 2 list to a function

Im playing around with CountryData and I want to pass it 2 lists as argument, listCountries = {...} and ...
4
votes
3answers
147 views

Symmetric list with maximum in center

How to sort a list, e.g. RandomInteger[{0, 100}, 50] that the Maximum is in the center and all other elements are placed symetrically in descending order around ...
3
votes
2answers
310 views

Binarizing a matrix

I have an image with a few bright pixels with the remaining ones very dark. The difference is in orders of magnitude. I want to binarize this matrix (corresponding to the image) making all values ...
3
votes
3answers
210 views

Speeding Up Replacing of Labels in Large Matrix?

I am Mathematica novice and am trying to find a fast way to replace labels in some rather large matrices (512x512 or 1024x1024) that have resulted from segmenting images with WatershedComponents or ...
29
votes
3answers
1k views

DeleteDuplicatesBy is not performing as I'd hoped. Am I missing something?

Déjà vu: a new-in-v10 function should provide a better solution to an old problem, but my enthusiasm is curbed when I run timings. This time the function is ...
0
votes
1answer
48 views

Interactively Manipulate SparseArrays or Lists

I'd love to use SparseArrayor List to group a set of parameters together in a function. ...
1
vote
1answer
82 views

Integers in Range have trailing decimal - how to remove?

I want to create a list like {0,0.2x,0.4x,0.6x,0.8x,1} If I try Range[0, 1, 0.2] x what I get is ...
2
votes
3answers
372 views

What is the order of faces on a D20? How can I optimize the order of faces on a D-n?

I am creating a customizable D20 for 3D printing using OpenSCAD, with the following code: ...
1
vote
0answers
64 views

deleteduplicates Delete elements of a list [duplicate]

I have a math problem about Mathematica, I am looking help from you. I hope that you could help me. The Math Problem: list= { {0,0,1},{1,0,0},{0,1,0} ,{1,2,3}}; ...
2
votes
2answers
50 views

How to further process a 2 dimensional list created with tuples

I created with Tuples[{{USD, EUR, JPY}, {UP, DOWN}}] the following result: ...
2
votes
3answers
203 views

How to display the indices/element positions of a ragged array?

I have a three-level ragged array like so: ...
2
votes
2answers
92 views

Adding a tree to a list of trees within a loop [duplicate]

I'm trying to write a function which for a list of trees checks if a given tree is isomorphic with any of the listed, and if not - adds it to the list. I tried to use both ...
1
vote
1answer
483 views

ListPlot[] code for CSV file not working

I have a CSV file with $9$ columns. I want to plot them in the following way. Column $1$ will be along the $X$-axis. Any point $(x_i, y_i)$ of $i$-th curve in the plot will have the $x$ value from the ...
4
votes
2answers
293 views

All possible pairs of two items

I have 4 different items {1, 2, 3, 4}. I want to obtain all possible pairs of two of the items. I have written: ...
5
votes
1answer
559 views

Why is there a huge performance gap using Map with more than 100 List entries

im using Map on a List like this: cube= {{1, 1, 1}, {1, 1, 2}, {1, 1, 3}, {1, 1, 4}, ... , {5, 5, 4}, {5, 5, 5}} Mapping the whole List with 125 entries takes ...
1
vote
1answer
135 views

Replace distinct values of list with values of another list

First of all I´m new to Mathematica; I´m trying to exchange distinct values of a list with values of another list (piecewise). I thought ReplacePart in combination ...
2
votes
2answers
191 views

How do I delete items at the same position from every sub-list within a list? [duplicate]

We have data in a list called megadata where megadata[[1]] for instance are the temperatures of each data point, ...
1
vote
1answer
109 views

Using Map in a function definition

I want to calculate the hessian of a matrix. So each element gets replaced by a 2 by 2 matrix. ...
3
votes
2answers
178 views

Elegant way for map a function over the columns of an array

I have an array data = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; And I want map Standardize over the column of the array. I use ...
4
votes
2answers
142 views

Get part of lousy data

I want to get part of large data. some part of this data is as follows: ...
5
votes
3answers
300 views

Command to insert item into list

Is there a command to insert an item into a list such that they form pairs? In other words to take InsertObject[{a,b,c},d] which will output ...
1
vote
1answer
338 views

DeleteCases that match partially [duplicate]

Say I have a list of strings L , L2= "some_text-to-delete" and I want to delete all the Li that match with "text" or "delete" DeleteCase only gives the ones that match exactly...
0
votes
4answers
154 views

Using levels in MapIndexed

I am trying to use MapIndexed to manipulate a matrix of data but I am having trouble getting the levels parameter to work the way I would like. Suppose that my data ...
11
votes
1answer
154 views

Is there is a design problem or documentation problem with FirstCase?

In version 10 the new function FirstCase can take up to 4 arguments (plus option). The third argument is a default value to be returned if there is no match: ...
8
votes
4answers
2k views

Swap elements in list without copy [duplicate]

I have a lists with 100,000 elements and would like two swap to entries without dublicating the list Example: ...
2
votes
3answers
799 views

Backsubstituting solution into FindRoot and Plot

I want to find roots from a transcendental equation using FindRoot as a function of a real parameter and then plot the solutions vs. the parameter. The following commands work perfectly: ...