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

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12
votes
7answers
526 views

How to use Union on list of lists without sorting them first?

If I do ClearAll[a, d] lsts = {{a, d}, {a, d}}; Union[lsts] I get the expected answer {{a, d}} but if I do ...
11
votes
3answers
170 views

Why can't I use Sequence to perform a Select like task?

Suppose I wanted to write down a list of $p^2$, for $p$ a prime between $1$ and $20$. I would expect Table[If[PrimeQ[k], k^2, Sequence[]], {k, 1, 20}] to work. ...
8
votes
2answers
321 views

Retrieving duplicates from nested list

Consider the following: data={{1,a},{10,a},{5,b},{4,c}}; In my case duplicates are defined when for {x1,y1} and ...
7
votes
6answers
184 views

How to join held Lists?

Let's say I have a = Hold@{2+2} b = Hold@{4+4} How can I get Hold@{2+2,4+4} ie join the two held lists ? More ...
7
votes
2answers
237 views

Programatically adding/retaining comments within a nested list

Is it possible to convert the following list of strings to computable numbers with the comments preserved? ...
7
votes
3answers
697 views

Why don't * and ^ work as I expected on matrices?

For example, this input... {{1, 2}, {3, 4}}*{{1, 2}, {3, 4}} produces this output... {{1, 4}, {9, 16}} and this input... ...
6
votes
5answers
244 views

Manipulating a sublist based on position

I have a huge list with huge sublists of the form list={{a,b,c,d},{e,f,g,h},{i,j,k,l}} I am looking for a way to manipulate these sublists based on the positions ...
6
votes
3answers
694 views

Ways to compute inner products of tensors

One way to evaluate the following sums is combining Table and Sum: $u_{abcd} = \sum_{e=1}^3 v_{aeb}w_{ced}$ $q_{ab} = \sum_{d,e=1}^3 v_{d e a}w_{deb}$ It will look like ...
5
votes
2answers
269 views

How to combine elements of two matrices?

Given two matrices m1 and m2, e.g.: m1 = {{a1, b1}, {c1, d1}} m2 = {{a2, b2}, {c2, d2}} How can one obtain the following? ...
5
votes
4answers
386 views

Leveling peaks in list

Consider the following: data={2,2,2,5,3,3,3,6,1,1,1,0}; In[1]:=result=MyFunction@data Out[1]:={2,2,3.5,3.5,3,3,4.5,4.5,1,1,1,0} ...
4
votes
1answer
319 views

Count sublists which match pattern

I have a list which looks like this: data={{12,0},{0,0},{20,1},{0,0}, {0,-1}}. Now I would like to count the number of sublists which: have both slots zero the ...
3
votes
0answers
73 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 ...
2
votes
1answer
321 views

RowReduce: Solving for the resource vector (a, b, c) in Augmented Matrix

Here are two examples: RowReduce[{{3, 1, a}, {2, 1, b}}] evaluates to {{1, 0, a - b}, {0, 1, -2 a + 3 b}} but ...
1
vote
4answers
189 views

List manipulation: position & max value combination

Starting with {{0, 0, 0}, {1, 1, 2}, {2, 3, 3}, {3, 4, 5}} I would like to get {{0, 2, 3, 5}, {1, 3, 2, 3}} where the ...
1
vote
3answers
257 views

ListPlot multiple datasets over same x-values

Is there a better way to enter my data into a list plot? ...
1
vote
2answers
198 views

How to blend some colors on a curve

I need to define a color gradient on a 3D curve, but I'm having some problems with this. Suppose we have a 3D curve defined as a parametric function of some real variable ...
1
vote
1answer
151 views

Syntax for integrating over limits specified by a Table

I wish to use NIntegrate to compute multidimensional integrals. However, I don't want to manually input the limits for the dimensions. I want to store the ...
9
votes
4answers
253 views

MapThread with non-rectangular lists

MapThread works fine and dandy with rectangular list structures: MapThread[f, {{{a, b}, {c, d}}, {{1, 2}, {3, 4}}}, 2] ...
6
votes
1answer
345 views

Finding all length-n words on an alphabet that have a specified number of each letter

For example, I might want to generate all length n=6 words on the alphabet {A, B, C} that have one ...
4
votes
1answer
135 views

Integrating a list of functions

For the purpose of this minimal example, let's say we have a list of functions, like this: f[y_?NumericQ] := {NIntegrate[z*y, {z, 0, 1}], a y} I want to ...
4
votes
1answer
279 views

Path queries for tree-structured data

Can anyone suggest documentation or tutorials for developing path queries and indices for (XML-like) tree-structured data? Suppose data is organized hierarchically in key->value pairs, eg: ...
3
votes
3answers
141 views

Picking certain pairs according to a condition [duplicate]

I'm a Mathematica beginner and can't find out a solution to my problem. I have a list of pairs of numbers, for example something like this, but much longer: list={{2., 3.}, {3., 2.}, {5., 4.}, {4., ...
3
votes
5answers
318 views

How to combine some elements of a list?

In order to simplify my expression, I face a list manipulation problem. For example, given the input list ...
3
votes
2answers
373 views

hexList[[1]] returns a list of decimal numbers

Sorry for not being clear about this question earlier. I appreciate the answers I got, but the edits I made should make the question more understandable. I have been working with hex in ...
3
votes
1answer
194 views

Exchange axes in ListLinePlot

I'm sorry to do this right off the bat, but I have the following set of data: ...
2
votes
3answers
177 views

Re-arranging / selecting of a data table very slow in For loop

My task is quite simple; I have a table of data like M = {{1,2}, {1,3}, {3,4}, {5,1}, {6,9}, {6,8}, {6,1}}; so the table is sorted with respect to the first ...
2
votes
0answers
289 views

Generating a function which outputs possible chemical reactions

I want to make a list of chemical reactions and I write them down in a $\require{mhchem}\LaTeX$ format. They are of the following form $$NA_n^i+MB_m^j \rightarrow \hat NA_{\hat n}^{\hat i}+\hat ...
2
votes
3answers
220 views

Taking only particular subsets and doing calculations

I have subsets formed from a list using the Subsets command and want to do a particular calculation, lets say subtraction using the ...
2
votes
1answer
169 views

List-operations only when restrictions are fulfilled (Part 2)

Consider the following: data={{{3544128000, 80}, {3544732800, 80}, {3545337600, 80}, {3545942400, 80}, {3545942400, 160}, {3546547200, 160}, {3547152000, 0}}}; ...
1
vote
1answer
148 views

Compile with array operations

When I use the function f with only the Module ...
1
vote
1answer
101 views

Format Preservation of FullSimplify on Indexed System of Autonomous Equations

I currently have a large system of 150 autonomous differential equations. I've indexed a more managable dummy system of identical form, using Part to reference ...
1
vote
3answers
152 views

Separate an array in two arrays, the even and odd terms being separated in these two arrays

How can I separate the odd terms in one array and the even terms in another array,i.e., go from a={1,2,3,4} to aeven={2,4} ...
1
vote
2answers
211 views

Thread over a nested list top to bottom until non-list elements are found

I have a nested list: list = {1, 2, {3, 4}, f[a], {2, h[b]}} I would like to apply a function g to all elements of the ...
1
vote
2answers
1k views

Calculating the distance between the coordinates in a list

I have a list of coordinates {{A[9, 4, 7], 0.0395174}, {A[1, 5, 0], 0.0163797}, {A[0, 7, 2], 0.0577425}, {A[2, 7, 5], 1.01313}} I want to find the distance ...
0
votes
2answers
107 views

Total elements of a list that have a common first element [duplicate]

Possible Duplicate: List-operations only when restrictions are fulfilled (Part 1) I have a set of data like: ...
18
votes
3answers
700 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 ...
17
votes
1answer
306 views

Underlying Algorithms for List Manipulation Functions

Does anyone know, or know of a link for the underlying algorithms used for list manipulation functions? Specifically: Union with and without the ...
27
votes
4answers
805 views

Filtering beat-to-beat heart rate data

From an experiment, I have a dataset of beat-to-beat heart rate data: a list of the time between each heart beat in [ms]. The data is measured using an infrared optic sensor at the finger tip. The ...
13
votes
4answers
2k views

Finding Local Minima / Maxima in Noisy Data

I'm trying to find local minima / maxima in noisy data, consisting of data values taken at certain time intervals. Ideally, the function should take a pair of lists (one containing time values and one ...
20
votes
5answers
5k views

How to find the phase difference of two sampled sine waves?

I'm trying to measure a phase difference between two Sine functions I've acquired with a computer. I'm uploading one of the .txt files with the data I'm working with here: txt file. To remove the ...
17
votes
6answers
4k views

How to find the position of elements in a list satisfying criteria

Say I have a list x={2,4,6,8,10} and I want to find out the positions of the elements that are greater than 7. ...
10
votes
10answers
534 views

Finding neighbors from list

Say you are given the following list: list={{3, 2, 1}, {3, 4, 2}, {2, 4, 1}, {1, 4, 3}}; Two numbers $x,y$, not necessarily distinct, are neighbors if one of the ...
25
votes
9answers
613 views

Sequentially numbering a nested list

I've got a nested list {a, b, {c, d}, e, {f, {g, h}}} which I want to magically transmogrify to ...
17
votes
4answers
259 views

Setting parts of a list

Suppose I have list a = Range[10] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} in which I want to set some elements to be a list ...
12
votes
10answers
597 views

How can I generate a nested array like this one?

Well, this is how the array looks like: I came up with this code: n = 10; Nest[ArrayPad[#, 1, 1 - #[[1, 1]]] &, {{1}}, n] /. {1 -> "*"} Any better ...
11
votes
2answers
188 views

Bug with SparseArray selector in Pick

I have created a notebook with two cells. This is the content of the first: ...
10
votes
2answers
418 views

Fastest way to check for List membership

I have a set of say 100 numbers {1,3,7,11,19,...3971}. All elements are previously determined. I want to check whether ...
8
votes
7answers
610 views

How to partition a list in a specific way

I have a list: a = {{1, 2, 3, 4, 1, 2, 3, 4}, {5, 6, 7, 8, 5, 6, 7, 8}}; Using Partition and ...
8
votes
4answers
259 views

Searching linked lists that contain lists?

Following the advice I've read here and other sites, I've been trying to use the Mathematica equivalent of a linked lists... ...
26
votes
2answers
592 views

DeleteDuplicates not deleting duplicates

It is not surprising that DeleteDuplicates[{5,5.}] returns {5,5.} because DeleteDuplicates ...