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

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5
votes
5answers
505 views

Efficient Indexed Sort

Suppose I have a preference for animals given by: orderOfAnimals = {"dogs", "cats", "fish", "elephants", "giraffe", "hamsters", "poodles"}; I'm given many data ...
0
votes
4answers
99 views

How to express “if any component in a vector satisfies that …” in Mathematica

For example, l is a list of vectors. I need to delete from l all the vectors with any component larger than 1. How should I do ...
0
votes
1answer
30 views

MapThread with incompatible length (How to Map twice in the same line)

l and b are two lists of vectors with different length. I need the list of vectors that is constructed by adding each member of ...
1
vote
4answers
175 views

Removing all values from a list that satisfy a given condition

Suppose I have a list, list = Table[{n}, {n, 1, 5}] (* list = {{1},{2},{3},{4},{5}} *) and I want to remove all values from this list that are greater than 3, so ...
0
votes
1answer
115 views

Error: in the part assignment is not a symbol [duplicate]

I am trying to set part of a Doubly-indexed list aInitialPopulation to cNumHeg. Specifically I am trying to set the 3rd part of the list aInitialPopulatiom[[cNodeNumber]] to cNumHeg. My (attempted) ...
4
votes
7answers
125 views

Distributing identifiers

I have a list that looks like this: {{"a",},{2010,0},{2011,10},{2012,27},{"b",},{2011,11},{2012,66},{"c",},{2010,19},{2011,20},{2012,}} I want to turn it into: ...
0
votes
1answer
73 views

Finding duplicates in a list [duplicate]

I have a list of integer, and I want to know if the list contains any duplicates. My code is working, but I feel there is a more straightforward way of doing this ...
2
votes
1answer
114 views

Excluding cases from Map

I'm doing operations of the form: PowerMod[#, -1, 126]+# & /@ Range[1, 125] When a number is not invertible, I don't want it to be included in the result ...
4
votes
2answers
93 views

How to sum values in the list that belongs to same week

I need to sum values that belongs to same week. For example, I have the list x with one column and n rows. Format: ...
3
votes
3answers
168 views

Finding the first position in a list that is over a certain value

Let's say I have the following list: L = {2,4,6,8,10} How can I get Mathematica to find the index position of the first value in the list that is over 4 (6 in ...
2
votes
3answers
77 views

How to manipulate one column of a table using the value in another column

Let's imagine I have the following table structure data = {{a, b}, {c, d}, {e, f}}; and I want to transform it into the following table ...
1
vote
3answers
172 views

A rule replacement problem: list -> list

Suppose I have a vector function f[x_] := {x[[1]]^2 - x[[2]]^2, Sin[x[[1]]] + Cos[x[[2]]]}; Then I want to make a list of gradients at some values: ...
1
vote
2answers
87 views

replace two elements in a list with the sum of those two elements?

I have a list: G[3] = {2, 4, 2, 4, 2, 4, 2, 4, 2, 4} (there's a 3 in there for the 3rd Prime) Recursively defined by: ...
1
vote
1answer
58 views

Finding list position in array [closed]

Lets say I have the list {{1,2},{1,3},{2,4},{1,3,5}} Is there a way I can get the positions of the lists starting with 1? ...
1
vote
1answer
92 views

Modifying a list of matrices with conditional statement

I have a list of around 100 matrices, that looks like this ...
7
votes
4answers
427 views

Computing a map between two lists

What I want is a little difficult to explain. So I try to it with an example. I have 2 lists, each of which has $(n-1)^2$ elements. Each element is an integers between 0 and $n-1$, inclusive. For ...
1
vote
1answer
112 views

Histogram from a list of matrices

I have a list of around 100 matrices, that looks like this ...
1
vote
1answer
88 views

How to form a variable from matrix elements

I have matrix with n rows and 2 columns, say m = {{x11, y12}, {x21, y22}, ..., {xn1, yn2}. Now, I want to form three new variables for example: ...
2
votes
2answers
121 views

How to delete certain unwanted elements from an array

Suppose I have an array like so array1 = {{Null,2,3,4,5}, {a,b,c,Null,e}, {w,x,Null,y,z}} Is there some way to selectively remove any element I ...
1
vote
1answer
52 views

Multiway Systems Rules List Management

I'm working with a multiway system and I have a number of different mutation rule lists. I need an efficient way of managing which rule lists I apply. Here is the basic multiway system code that I'm ...
1
vote
2answers
148 views

Symbolic combinations

If I have 3 lists: {a,a},{b,b},{c,c}, then the desired output is ...
1
vote
2answers
51 views

Exporting mixed data of matrices and vectors / lists

thank you for reading my question. I have a problem trying to export mixed data from Mathematica. I have different matrices and vectors, which should be combined to a output file. Here a ...
3
votes
1answer
169 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
3answers
198 views

Pare down list recursively

What is the best way to pare down a list whereby the $n$th number is removed from the list recursively? This ...
1
vote
0answers
109 views

How to create a complex variable from dated list values

Can anyone help me to construct a variable "PI" from values of variable x. Variable x represents a group of two time series rj and ri on equal dates(joined two dated lists with states).Variable x have ...
5
votes
4answers
382 views

How to extract a part of matrix satisfying certain condition(s)

I have a following matrix ...
2
votes
4answers
462 views

Selecting every n-th element from a list [closed]

I have a list: data = {4, 5, 7, 8, 9, 5, 3, 2, 1, 2, 13, 12}; I want to take those elements in the list which are located at equal distances, say, every third ...
3
votes
2answers
103 views

MapThread problem

I would like to do the following: ...
4
votes
3answers
161 views

Extracting columns from multidimensional list

Perhaps a very easy question but I posted this on the Wolfram Community and didn't get any answer.. Suppose I have data like: ...
3
votes
1answer
134 views

Programming for matrix manipulation

I want to write a programme which operates on nd x nd matrices. The programme looks the matrix as a n x n block matrix where ...
4
votes
2answers
138 views

Can't figure out how to apply these functions repeatedly

I have the following problem, and even though I've tried Fold & Inner, Sow & Reap, et al. I can't figure out the clean way to do this. Here's the problem. I have a list that starts as ...
3
votes
2answers
64 views

Fast functional method for multiplying duplication numbers in a large list

Consider a list of symbols: mySet = {a, b, b, c, a, b, c, d}; I would like to form the product of duplication numbers. In the example above, I have 2 ...
2
votes
3answers
94 views

Manipulating array

I have got an array like this: A = {{{1, 4, 5}, {3, 7, 15}}, {{5, 6, 9}, {7, 8, 2}}, {{9, 10, 1}, {11, 12, 3}}} I make differences in each sublist a following ...
1
vote
2answers
128 views

How to select states with equal times

Can anyone show me how to select the states that have equal times-dates. For example, i have two time series. First that have 10 observations, say from 2014/10/1 to 2014/10/10, and second that have 7 ...
1
vote
2answers
131 views

Replace list of symbols in an expression

I have an expression: exp = a+b+c and a list containing all the symbols of my expression: syms = {a,b,c} and I would like ...
0
votes
4answers
86 views

Conditional combining of nested lists

I have two nested lists like those {{a,A},{b,B},{c,C}...{z,Z}} {{a,1},{c,2}...{t,12}}. I want to combine them to get a new list that looks like this ...
-1
votes
1answer
105 views

Rotate points by 60° in 2D

I wrote this code, to rotate a list of points 60° about the first point in the list in 2D, but Mathemtica says: "Recursion depth of 1024 exceeded."
7
votes
5answers
1k views

Check if two lists are equal in any order

Suppose I have two lists, how can I efficiently check if the two lists are identical up to permutations of the elements? For example I would like the function to output: ...
2
votes
2answers
131 views

Matching a case when one element in a pair is Null

I've got a dataset of laitutdes and longitudes. Unfortunately, some of the dataset was from when a time when lat/longs weren't constantly recorded. So I need to remove the invalid data before working ...
6
votes
2answers
102 views

Mathematical operation on two lists by a “key” [duplicate]

I'm a complete newb here. Just looking for direction. I've got two lists like this... ...
1
vote
1answer
67 views

Summing subsets of array

I have an array farr, size Nx*Nx. I have a function frk that maps index {n,m} to an integer (approximately ...
0
votes
1answer
65 views

Loops for Unit Root Test

I want to compute some unit root tests on a data generating process. I already split the sample in 100 single samples, but how can I do a unit root test on all of them and store the results in another ...
2
votes
3answers
140 views

Concisely returning a position in an array with an index variable [closed]

We have an array and an index in the array: exampleArray = Table[{a, b, "q"}, {a, 1, 10}, {b, 1, 10}]; arrayIndex = {5, 4}; Very simply, we can return the value ...
2
votes
2answers
52 views

replace an interval of values [duplicate]

I want to replace values in an interval [a,b] by 0 in a list of values. Example: {{.5,.2,.49,1,1},{.49,.5,.495,1}} I want to get: ...
3
votes
4answers
159 views

How to Remove Undirected Edges that are the Same [duplicate]

Given: theData = {1 <-> 2, 2 <-> 3, 2 <-> 1} I would like to remove any duplicates where I define a duplicate to be: ...
2
votes
3answers
79 views

How to get an element of a list , which is computed out of substituted variables?

What is the best way to get the element of a list, which is computed out of substituded variables? For example one wants to get the first element of the first row of ...
2
votes
1answer
186 views

DateListPlot with multiple data sets and incongruous timelines?

I am using Mathematica to analyze some sales data for my company. (A copy of the available data is here.) We are trying to analyze the sales trends for each month by item. DateListPlot works well ...
4
votes
3answers
346 views

Changing the x-axis for ListLinePlot with more Lists

I'm fighting with a seemingly very simple problem: I have two lists of data, and want to plot them with ListLinePlot. The two lists are only data-points, therefore ...
11
votes
3answers
308 views

What is the best way to flatten a linked list with lists as values?

By following the advice on this site I have ended up with a linked list like the following: acc = {{1, 2}, {{2, 3}, {{3, 4}, {{4, 5}, {{5, 6}, {}}}}}}; This was ...