# Tagged Questions

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

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 ...
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: ...
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 ...
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 : ...
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 ...
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 ...
4answers
191 views

### Minimum and maximum values under conditions

Let's create some sample data ...
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, ...
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, ...
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: <...
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 ...
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 ...
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...
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: ...
1answer
469 views

### How to slice TimeSeries data?

When retrieving curated data, v10 now returns TimeSeries objects. For example, ...
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.
4answers
170 views

### Replacing more than one element from a Sublist

The following expression allows me to extract the value of x and y: ...
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: ...
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: ...
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 ...
1answer
145 views

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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 ...
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 ...
2answers
289 views

Question2:: ...
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 ...
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 ...
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 ...
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 ...
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 ...
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. ...
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 ...
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: ...
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}}; ...
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: ...
3answers
203 views

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

I have a three-level ragged array like so: ...
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 ...
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 ...
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: ...
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 ...
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 ...
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, ...
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. ...
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 ...
2answers
142 views

### Get part of lousy data

I want to get part of large data. some part of this data is as follows: ...
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 ...
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...
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 ...
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: ...
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: ...
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: ...