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

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7
votes
5answers
327 views

LengthWhile until first duplication

I have the need to trim each of a large number of potentially very long lists (10^6+ elements) to the length where the last occurrence of any distinct element happens, or said another way, where the ...
1
vote
1answer
98 views

Experiment with TagSetDelayed involving Part

Reading Associating Definitions With Different Symbols, I was intrigued by this: You can think of upvalues as a way to implement certain aspects of object-oriented programming. A symbol like ...
8
votes
7answers
1k views

How to select all elements above the main diagonal of matrix?

How to select all elements above the main diagonal of matrix? I need to create a list of them.
2
votes
2answers
136 views

Elegant way to rearrange year/date table into time series/values

I often have data in the form of YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 1950 -1.022 -1.146 -1.289 -1.058 -1.419 -1.36 -1.334 -1.05 -0.578 -0.395 -1.151 -1.248 1951 ...
2
votes
2answers
178 views

How can I thread lists of different sizes?

What I need is the equivalent of Maple's zip(+, A, B, 0). Sure I can get it with: ...
2
votes
1answer
297 views

Selecting every last element of a nested list

I couldn't find a similar question so I decided to ask this one. I have a nested list with many sublists of equal length. To make things easier let's say it's like that: ...
15
votes
4answers
2k views

Semi prime numbers

The high school textbook I am using has the example of semi-prime numbers. They wanted students to find (by "perspiration") all the semi-prime numbers less than $50$ (for a question on set theory). ...
2
votes
1answer
146 views

Intersection does not take list of lists

The function Intersection takes a number of lists (sets) and finds their intersection. However, the precise input is ...
1
vote
2answers
249 views

Sorting lists element by element [duplicate]

I have a problem regarding list sorting. Let's say I have a list of lists obtained using Subsets[], of the form ...
0
votes
2answers
176 views

Specifying an array that may have an unknown number of entries [duplicate]

Say I'm running some process of unknown duration, and during the process, I need to periodically record the state of some variable. If we knew exactly how long the process took, we could simply ...
4
votes
3answers
372 views

Fast method for combining two lists

I have two lists, v1 and v2. Each element of the lists may be positive or negative. I want to create a list ...
2
votes
7answers
370 views

How to replace plus sign by comma

I want to replace plus by comma and the order of numbers in the list should be in increasing order. Example: a1 + a10 + a11 + a13 + a2 + a27 + a28 In this ...
1
vote
1answer
86 views

Evaluating the tensor product many times for a given list

I need to evaluate the tensor product 10 times in a given list( {g,e,r}) Here I have evaluated for 3 times... ...
1
vote
1answer
5k views

Table - find index of the maximum element [duplicate]

Let's suppose that I have table t = {1.23, 3.4, 10, 34, 1.78, 0.98, 12.56}. To take the biggest element I can use Max[t] ...
1
vote
1answer
830 views

ListPlot doesn't shows all points [closed]

I have a table: p1 = Table[(Binomial[2000, k]*StirlingS2[1386, k]*k!)/(2000^1386), {k, 1, 1386, 1}]; I used ListPlot[p1] ...
2
votes
3answers
199 views

Counting instances where the two identical characters are at the same positions in two strings

Let $s_a$ and $s_b$ be two strings over a $q$-ary alphabet. For each character $(c_1,...c_q)$ in the alphabet, I'd like to return a pair of values $(r,k)$ where $r$ represents the count for the ...
0
votes
1answer
109 views

Error about limit MaxExtraPrecision

After my evaluations I have an error: N::meprec: Internal precision limit $MaxExtraPrecision=50. reached while evaluating ... ...
8
votes
6answers
250 views

Faster list duplicate 'limiter'

Given some list, e.g., {5, 3, 2, 3, 1, 0, 1, 3, 5, 5, 4, 5, 1, 2, 5, 2, 2, 0, 1, 4}, I need to limit the duplicates, if any, to an arbitrarily chosen number. The ...
1
vote
2answers
113 views

Choosing a position in an array with uniform random probability conditioned on it having a specific element

I have an array exArray with two types of integer elements: 1 and 2. I'd like to choose a ...
2
votes
2answers
74 views

Specifying an array with a specific number of copies of two elements

To specify an array of length L in Mathematica, where each entry is someElement, I'm accustomed to writing: ...
7
votes
5answers
372 views

Find positions of duplicates that are neighbours

Assuming the following list {1,2,3,3,5,6,3} I would like to get the position of values that are next to each other and are duplicates. That is, the output should be {3,4}. Thank you for any help. ...
7
votes
3answers
264 views

When does a list contain only ones?

I am starting with a list of length n that contains all -1's. For instance, when n = 6 the list is {-1, -1, -1, -1, -1, -1}. I ...
19
votes
5answers
1k views

Moving maximum function?

How can I construct a moving maximum function? For example, if I have a list of 12 values: { 5, 6, 9, 3, 2, 6, 7, 8, 1, 1, 4, 7 } and I want to maximize over 3 ...
1
vote
3answers
213 views

Distinguishing slots in a function mapping Position across a list

Suppose that I have a list myList that has more than one level. Here is an example of such a "data structure": ...
2
votes
3answers
127 views

Quickly plotting (number of events) vs. (time) for a very large number of events encoded as pairs of real numbers representing start and end times

I have an array that looks like the following: exampleArray = {{t1,r1},{t2,r2},{t3,r3},{t4,r4},{t5,r5},...}; Where each pair of real numbers $(t_k,r_k)$ ...
22
votes
5answers
731 views

More efficient way of generating list of occurrence counts?

Given a list, e.g., target = {a, b, c, b, c, d, c, d, e, f, a, h, g}, I want to generate a list containing the occurrence count of the corresponding element of the ...
0
votes
1answer
84 views

how to filter out numbers of specific type in a table

I am working with a way to generate a table of some numbers, but the one functions could return the complex numbers which I don't want. I am going to filter out the complex numbers. The only way I can ...
1
vote
2answers
174 views

How to create automatically some matrices for symbolic manipulation?

I want to create in an automatic way some matrices to do symbolic calculations with them. They look like these: $$ \left( \begin{array}{cccc} a & 0 & b & 0 \\ 0 & 1 & 0 & 0 ...
5
votes
4answers
1k views

Select a repeated element in a list

I want to select all elements that repeat 4 times in the list. I propose this code ...
4
votes
4answers
1k 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
1answer
279 views

MapThread multiple functions onto multiple lists

I'm trying to learn the functional style which seems to prevail in Mathematica. I'm having trouble accomplishing the following: Let's say I have multiple lists of arbitrary data (using two lists ...
5
votes
5answers
421 views

Counting 'False' values at the ends of a list

I have table like this: t = {False, False, False, 4.5, 6.789, 1.23, 0.98, False, False} and I want to know how many False values I have at the beginning and at ...
2
votes
1answer
167 views

Using DeleteCases with multiple AstronomicalData properties

I am attempting to use AstronomicalData and DeleteCases together to remove invalid cases of two properties while listing the ...
1
vote
2answers
128 views

Computing lists using AstronomicalData

Edit: Initially in my question I asked how I could search the database of AstronomicalData["Exoplanets"] and return 2 filtered values that only contained valued ...
0
votes
2answers
169 views

Associate the elements of a table

I have a table form as: table = {{a, 6}, {b, ff}, {c, 2}} I want to associate the first element of each pair from the table to the second element of the pair as ...
0
votes
0answers
28 views

Threading a single abscissa through a list of ordinates [duplicate]

Suppose that I have the following list, called list. list contains elements X, ...
0
votes
2answers
77 views

How can I make my output to be added to an existing list?

v = {{0, 0, 0}, {1, 0, 0}, {1, 0, 1}, {0, 1, 1}, {1, 1, 1}} For[i = 1, i < 6, i++, For[e = 1, e < 6, e++ 1, Print[Mod[v[[i]] + v[[e]], 2]] ]] I ...
1
vote
1answer
115 views

Testing a List inside of an Table if it is != 0 [duplicate]

I'm new to mathematica so I hope this is not a too stupid question, but I couldn't find a solution in the mathematica documentation. I've got a normal table, initialized with "0" as entries. In the ...
5
votes
2answers
673 views

How to plot several functions without jumping? (multiple eigenvalues of a system as functions of 2 parameters)

I've been working on this research problem for months with some success by no global/proper solution to the problem. So I have square, Hermitian matrices of various sizes ($8,20,38$ dimensions) with ...
3
votes
2answers
319 views

Finding positions of multiple elements in lists

I realise that Position[{2, 4, 8, 16, 32, 64}, 4] will return {{2}} I would like to do something like this: ...
1
vote
1answer
100 views

How to convert each pair of { and } into ( and )? [duplicate]

I am a learn-by-example person. I have no idea to change every { and } to ( and ...
1
vote
1answer
544 views

How to convert the following list into a LaTeX table?

How to convert the output of the following code In[43]:= Func[x_]:=Select[Range[x],Total[IntegerDigits[#]^3]==#&]; Func[1000] which is Out[44]= ...
11
votes
10answers
750 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 ...
10
votes
3answers
482 views

Zero-dimensional matrices

In a recent Mathematica project, $(n \times 0)$- and $(0 \times n)$-dimensional matrices have suddenly become a frustratingly common edge case for me. For instance, consider the following two ...
10
votes
3answers
250 views

Can I return lists with different dimensions from a compiled function?

Sometimes I'll need several lists with different dimensions to be returned by a compiled function, but compiled function will fail if an irregular list contained: ...
4
votes
4answers
338 views

Deleting powers of a common prime except the highest one from a list with further only primes

In a list with factors of which most are prime, some are integer powers of some common prime as base. All the powers from 1 to ...
0
votes
2answers
294 views

Replace all elements of a list

I have a set that looks like: s = {{1, 2, 3} -> 9, {4, 1, 9} -> 9, {3, 7, 3} -> 1}; Now, I want to replace each element of the set by the lhs of "...
5
votes
1answer
189 views

MapThread over large graph

I am trying to build a very large graph with approximately $16\,000\,000$ edges, each being a two-dimensional integer vector. I have a list of edges in the form $\{\{e_{11}, e_{12}\}, \{e_{21}, ...
1
vote
2answers
276 views

Deleting parts from a nested list

I have a very long nested list. Here is a short example: list = {{1.2, {1, 1, 1, 1}, {2, 2, 2}}, {0.9, {3, 3, 3, 3}, {4, 4, 4}}, {1.4, {4, 4, 4, 4}, {5, 5, 5}}} ...
13
votes
6answers
680 views

Elegantly split a matrix into positive and negative parts?

I have a matrix $M$ of real components, and I want to split it into two matrices $M^+$ and $M^-$ of the same dimensions as $M$, where $M^+$ contains the positive components of $M$ (the remaining ...