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

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0
votes
2answers
46 views

Troubleshooting Program Meant to Swap Elements

I wrote a program that is supposed to take a list (of arbitrary length) of pairs of the digits of binary numbers (e.g. ...
6
votes
2answers
187 views

Is there a built-in equivalent to Python's enumerate?

Python's built-in function enumerate takes an iterable over $(a_0, a_1, \dots )$ as argument and returns an iterable over the sequence of pairs $((0, a_0), (1, ...
3
votes
2answers
120 views

How to speed up Select with MemberQ for large lists?

I have two large lists: list1 and list2. I would like to select elements of list1 only if they appear in list2. Since the list1 has dimensions of (335000, 2) and list2 : (122000, 4), it's taking a ...
0
votes
1answer
50 views

What is this Counts[] output format?

I need to create a list of the distinct elements in a list along with the number of times each appears. The function Counts[] is supposed to do this, but it puts the results in some weird format I've ...
1
vote
3answers
85 views

Partitioning List Into Sublists of Length 2 With The Pairing Being Random

I've done a bit of Googling with hopes of finding an answer, but to no avail. I'm looking for a way that I can have Mathematica take the elements of a list, say ...
1
vote
1answer
68 views

Tiny question about Indexed[x,n]

Maybe I should apologize for this silly question, but the documentation for Indexed is very short and not explicit. I have an equation with variables ...
3
votes
2answers
93 views

Help with list manipulation

I often need to merge two lists like the following: $A=\{\{0.1\},\{0.2\},\ldots,\{1\}\}$ $B=\{\{x_1\},\{x_{21},x_{22},x_{23}\},\{x_{31},x_{32},x_{33}\},\ldots,x_N\}$ in a way to ideally obtain a ...
0
votes
3answers
65 views

Logarithmic x-axis for ListPlot?

I have a list of points that I am trying to plot. Is there a way to make a ListPlot where the y-axis increases normally by 1 every interval but the x-axis ...
0
votes
1answer
55 views

Mathematica Code Involving For Loops Not Completing All Iterations [closed]

First of all, thank you for taking the time to read this. I'm working on a portion of code related to the genetic algorithm that is not producing the expected results. What the code is supposed to do ...
1
vote
2answers
68 views

Create a table of Mean Values and Standard Deviations from data list

I need to create a table of the Mean Values and Standard Deviations of 18 columns of data from a table. I know how to compute the Mean and Standard Deviation for the different columns, but am unsure ...
11
votes
1answer
227 views

Map efficiently over duplicates in list

I am interested in mapping a function, f over a (long) list which contains duplicates. Since this function takes a while to evaluate I would like to make use of ...
5
votes
1answer
112 views

Find all “chains” in the poset of divisors

I want to input a set of divisors of an integer $n$ and return all subsets of these divisors ${d_1,d_2,...d_k=n}$ such that $d_1$ divides $d_2$, $d_2$ divides $d_3$, ... and $d_(k-1)$ divides $d_k$. I ...
1
vote
1answer
46 views

Using HoldForm for a changing list

I have a 'list' of the form an expansion: F = (A[1] + A[2])(B[1] + B[2]), such that F[[1]] produces the result ...
11
votes
2answers
2k views

How to use “Drop” function to drop matrix' rows and columns in an arbitrary way?

The built-in function "Drop" can delete a Matrix's row and column. Typical syntax for "Drop" is as follows: Drop[list,seq1,seq2...] But what if I want to drop a ...
2
votes
1answer
205 views

Rearranging a biclustered matrix

I currently have a $77\times 38$ matrix, and I have used a clustering algorithm to cluster the row data and column data. The rows and columns of my matrix correspond to a list of country codes (not in ...
8
votes
4answers
140 views

Handy / flexible directory tree operations

Is there any shorter / more handy / more flexible way to get directory tree as a nested Rules/Associations list? I tried to incorporate ...
5
votes
1answer
476 views

Generating random symmetric matrix

Suppose first that I want to generate a matrix whose elements are independent and identically distributed (i.i.d.) with distribution dist. This is easy: ...
1
vote
0answers
49 views

Problems with indexes in a Do-cycle and CoefficientArrays

I have a system of linear equations with variables $A_n$ and need its coefficients in a matrix form (Transform linear system into a matrix form). I'm trying to do that through a ...
-1
votes
1answer
144 views

Strange bug involving a list, “Objects of unequal length” [closed]

sortedTally is a list generated from Tally sortedTally[[1]][[1]] is a list If I print: ...
4
votes
2answers
182 views

How to convert a list of 3D points to a list of distances?

How do I apply a function (this case EuclideanDistance) between element i and i+1 on a list ...
5
votes
3answers
110 views

Levelspec range with negative levelspec

Documentation states A negative level -n consists of all parts of expr with depth n. However, it is not clear what do ...
2
votes
1answer
88 views

Grouping large dataset across a large range of values

I have a large data set that I would like to group based upon the quantiles of one specific column. My test data set is about 2.1 million rows by 9 columns (the actual data set will be much larger). ...
1
vote
3answers
132 views

List of prime powers

I have a list of not necessarily distinct prime powers. For example: {2,3,4,25,2,3}. I want to combine (multiply) the highest prime powers for each prime. In this case 25*3*4 = 300 since 25 is the ...
29
votes
9answers
739 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 ...
8
votes
3answers
317 views

Numbering nested list according with Depth (or Level)

(This question is slightly similar with Sequentially numbering a nested list, but not exactly the same.) What I want Say I have a nested list ...
1
vote
1answer
74 views

Pattern matching list of elements with different heads

I have a function, which I want to accept only a list of kind of elements belonging to a group. The task comes down to finding an elegant pattern suitable for easy to read function prototype. As an ...
0
votes
4answers
123 views

Do loop not working as expected

I am trying to get rid of data in a list. Every three elements I want to delete. Example below: ...
3
votes
2answers
111 views

Replace missing data

I have vectors of equal lengths where I want to replace the zeroes (missing data) with their preceding values. So far I have written: ...
5
votes
2answers
647 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 ...
0
votes
0answers
38 views

Constructing a function for expanding general $n$ products

I have the following quantum mechanically motivated product: $\langle0\vert(A_1b_1 + A_2b_2 + A_3b_3)(B_1b_1 + B_2b_2 + B_3b_3)(C_1b_1 + C_2b_2 + C_3b_3)$, where $b_i$ is an annihilation operator ...
12
votes
6answers
812 views

Deleting Lonely Numbers From a List

Suppose I have a list of integers like so: list = {1,2,5,6,8,10,11,12,14,16,17,18,19}; I'd like a function that will take this list and return a new list with ...
0
votes
1answer
54 views

How to count column occurrences in a matrix?

I have a matrix of data, and I want to count the number of columns that match, and have some way to organize them by frequency. But I don't want to count the entire column, but consider the matrix ...
0
votes
3answers
115 views

How to cross over the corresponding elements of matrices (genetic algorithm) [closed]

I'm working on some genetic algorithm code, and I'm seeking help to select the corresponding elements of a matrix in order to perform crossover on the chromosomes in population of individuals I want ...
0
votes
0answers
23 views
4
votes
3answers
99 views

How to evaluate an expression over a particular list of tuples?

NOTE: This question is very similar to this one but I realized reading at the answers that I made a mistake in the equation AND I was not clear enough about what I need (my apologies): I want to ...
4
votes
5answers
290 views

Pattern matching in nested lists

I'm sure this has been asked before, but I can't find the right combination of search keywords to find it. Apologies. I want to do a ReplaceAll on a list of lists, ...
0
votes
1answer
75 views

How to identify and remove errors in a list

After some searching, I did not find a solution to the following problem, which in my thinking should have some very easy/efficient solution. I'm looking at a list of images (faces), that I want to ...
1
vote
2answers
90 views

List Operations: how to combine two lists (pattern given)

Two lists (matrixes) are given: a = {{x1, y1}, {x2, y2}, {x3, y3}}; b = {{u1, v1}, {u2, v2}, {u3, v3}}; Expected return: ...
3
votes
3answers
83 views

Identifying locations of entries in an array

If I’ve got a big array displayed in Mathematica, is there a way for me to select a particular location on the screen and have Mathematica tell me “You’ve selected the entry in row 137 and column 92” ...
7
votes
4answers
478 views

MovingAverage to include the average of the first and last elements in a list

Is there any way to take the average of pairwise elements in a list? Example: Given the list list = {a,b,c} I'd like to generate the list ...
1
vote
2answers
163 views

Complex numbers from two arrays with Real and Imaginary parts

I have two arrays, containing the real and imaginary parts of a list of complex numbers. Re = {{Re_number1},{Re_number2},...} Im = {Im_number1},{Im_number2},...} ...
0
votes
2answers
45 views

Selecting the maximum value from the results returned by NSolve

I'm trying to select the maximum value from the answers Mathematica 7.0 is getting from a simple basic NSolve algebric equation : ...
1
vote
3answers
176 views

Listing elements starting from 0

The first element in a list v in mathematica is denoted by v[[1]] and subsequent ones are then ...
-1
votes
2answers
58 views

Convex Combinations of List Elements

Let's say I have two lists $L_1=\{a_1,...,a_5\}$ and $L_2=\{b_1,...,b_10\}$. Is there an easy way to make new lists from convex combinations of these two lists' entries? Let me be more specific: 1 ...
0
votes
1answer
55 views

How to find the starting point of an oscillation (with noise)?

I've got a series of coordinates which start to oscillate from some time (and with noise), like this: ...
2
votes
1answer
53 views

How to show steps of “For” command

I wrote the command: list = RandomInteger[{0, 10}, {9, 3}]; For[i = 1, i <= m, i++, element=Total[ list[[i]] ] ] How can I make every step visible? If I ...
0
votes
1answer
54 views

Position vs Part [closed]

What's the difference between Part and Position? How can I "move" from the form used by Part to that of Position (and vicerversa?) Thanks!