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

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9
votes
1answer
237 views

Creating a number based on given conditions

In the grade 7 math curriculum here in Alberta we teach divisibility. I'm trying to write a program to create questions based on the idea of a student being given say, 4 digits, and then choosing ...
9
votes
1answer
155 views

Lexicographic ordering of lists-of-lists?

I was surprised to discover that Mathematica does not sort lists-of-lists (LLs) lexicographically by default. For example, applying Sort to ...
9
votes
2answers
298 views

Complement on pre-sorted lists

Is there any way to instruct Complement to skip the sorting part? If the answer is no (likely), the next question would be: how can I remove from a sorted list ...
9
votes
2answers
398 views

What is the fastest way to get the nth distinct permutation of a list?

What is the fastest way to write a function nthPermutation[xs_List, n_Integer] which is equivalent to Permutations[xs][[n]] but ...
9
votes
2answers
185 views

Checking if one partition is a subpartition of another

Say I've got two partitions of a list (not necessarily containing numbers, and not necessarily distinct), and I want to check that one is a subpartition of the other. Let's look at some examples: ...
9
votes
2answers
959 views

Flatten at a certain level

In an earlier question the brainteasing fourth syntax variant of Flatten was discussed. I see that with ...
9
votes
1answer
124 views

ListConvolve Memory Hemorrhage

I wrote a routine that convolves an impulse response array with a test array and checks for the RMS difference between that convolution and a data array. I do this iteratively so that I can modify the ...
9
votes
0answers
232 views

How to merge Datasets representing matrices with named rows/columns?

I am working with square (non-symmetric) matrices with named rows and columns. The data I receive is sometimes messy and rows/columns may come in various permutations. I usually need to ...
9
votes
0answers
258 views

Using Compile to speed up Function with PermutationProduct

I have the following fairly simple routine dot involving PermutationProduct that I wish to speed up using ...
8
votes
8answers
734 views

Replace interior of matrix with zeros

I have f.e. the following square matrix: ...
8
votes
10answers
355 views
8
votes
5answers
375 views

How to distinguish between lists and values?

I have a (hopefully small) problem with some numerical integration algorithm, more specifically I want to integrate the imaginary part of a complex valued function, e.g. ...
8
votes
7answers
834 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
5answers
365 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 ...
8
votes
8answers
492 views

How to use Map inside MapThread?

Given this input lst1 = {{a, b, c}, {d, e, f}}; lst2 = {1, 2}; and the goal is to generate this output ...
8
votes
7answers
802 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: ...
8
votes
3answers
881 views

Checking for duplicates in sublists

I have a list with contains entries that are length 8 sublists,i.e. L1={{a1,b1,c1,d1,A1,B1,C1,D1},{a2,b2,c2,d2,A2,B2,C2,D2},...} and so on. Now, in my problem two ...
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.
8
votes
3answers
1k 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... ...
8
votes
3answers
559 views

Creating a simple function to compute the average of the difference between pairs of elements in an array

I have a list of the form: {{{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}, {{9, 10}, {11, 12}}} How can I create a function which will take each set at the highest level of ...
8
votes
4answers
469 views

Partitioning a list by recursion (Programming Paradigms via Mathematica (A First Course))

I am working through the course Programming Paradigms via Mathematica. One of the homework exercises for the section Recursion I: Passing the Buck is as follows: Use recursion to partition a ...
8
votes
7answers
300 views

Input a square matrix and return a list of the matrix entries read by antidiagonals

I have a square matrix: {{1,2,3},{4,5,6},{7,8,9}} and I want to get a list: {1,2,4,3,5,7}
8
votes
3answers
583 views

Sum over binary digits of integer

This might seem like a simple enough question but Mathematica seems to simplify inadequately here: How would you sum over the digits of an arbitrary binary number? I already tried this: ...
8
votes
4answers
336 views

Generate PrimePower counting function

Is there a way to generate a counting function for prime powers - i.e. to create a similar function to PrimePi, but including prime powers. The following will, of ...
8
votes
6answers
224 views

Custom Matrix product

I have a list: list1 = {{{a1, a2, a3}, {b1, b2, b3}}, {{c1, c2, c3}, {d1, d2, d3}}}; I want an operation that gives me: Is there a built-in way of doing ...
8
votes
5answers
513 views

Computing the equivalence classes of the symmetric transitive closure of a relation

I have a list of pairs, for example: ...
8
votes
2answers
249 views

How to generate Intervals from a given list?

If I have a list list={3,7,4,5,1} how to get the List of Intervals /Ranges result = {{1,3},{3,4},{4,5},{5,7}}
8
votes
4answers
895 views

How make f[{x,y}] evaluate as f[x,y]? [duplicate]

I frequently encounter the situation where I have a function of two real variables defined, e.g.: f[x_, y_] := 9 - x^2 - y^2 But then I need to feed into ...
8
votes
3answers
884 views

How can I get a running sum for a list?

I've got following data I'm reading from a file: ...
8
votes
2answers
385 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 ...
8
votes
5answers
309 views

Wrapping a function in count

I am working through the Programming Paradigms via Mathematica (A First Course) and am attempting to answer the following: Use recursion to count how many times the argument can have its square ...
8
votes
4answers
458 views

Gather list elements by index

The following list has some elements that are labeled. For example {1, 2} -> 1, {-1, 3} -> 3, etc: ...
8
votes
3answers
319 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 ...
8
votes
3answers
686 views

how to efficiently apply function to all pairs of a set (and collect the results)

To build a graph, I need to apply a function f[a_, b_] to all pairs of a list (3500 elements). The function itself returns a link ...
8
votes
3answers
206 views

Select and Blank

I try to filter sublists of a list which match a pattern. test = {{"String1", "a"}, {"String2", "b"}, {"String3", "a"}, {"String4", "a"}}; The result should ...
8
votes
3answers
1k 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 ...
8
votes
4answers
283 views

Check in a series if there exists adjacent values with less than a certain number of missing values

I'm working with a large number of series of different experiments, where there exist a lot of experiments where there are no entries. I now want to draw a sample where there should exist at least ...
8
votes
3answers
305 views

How to remove a line of a matrix if not all elements are numeric?

I have a matrix a n columns and m lines. I'd like to efficiently remove the lines that are not entirely composed of numeric ...
8
votes
5answers
223 views

How to do DateDifference on table items containing dates

I have a Table with data in form {{date}, value}: ...
8
votes
4answers
408 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 $m\times n$ ...
8
votes
5answers
309 views

Refer to next element of list when iterating using Map [duplicate]

Is it possible to refer to the next element of the list when I'm using Map or should I always use For in this case? For example ...
8
votes
4answers
153 views

Mark selected sub-lists in the list they were selected from

I've got this simple problem with two lists. I select some items from a list, but I want to visualize the difference between the previous list and the list that I create with ...
8
votes
3answers
4k views

Summing along rows or columns of a matrix

I have a list of rows in database such as {{a,b,c}, {d,e,f},{g,h,i}} I want to be able to add each row across and each column down (like a spreadsheet). In other ...
8
votes
5answers
313 views

How can I find these patterns' signatures?

I think I can explain it best starting with an example. I have the following lists: ...
8
votes
5answers
991 views

Generating an Ulam spiral

An Ulam Spiral is quite an interesting construction, revealing unexpected features in the distribution of primes. Here is a related topic with one answer by Pinguin Dirk, who has provided one ...
8
votes
3answers
201 views

Preserve information in flattening a nested list

I have a series of lists in the form below: list={ {1,1} , {2,2}, {3,{3,1},{3,2},{31,{31,1},{32,2}}} } Its a nested list which the dimension is changing case to ...
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 ...
8
votes
3answers
171 views

How can I use the overhang argument to Partition to avoid using PadLeft and PadRight here?

Say I have a list of values v = {v1, v2, v3, ... }. I need to partition these values to perform operations with a sliding window (think ...
8
votes
2answers
255 views

What does IndexBy do and how exactly does it work?

I just saw the function IndexBy in the autocomplete suggestions and I was curious to know exactly how it works. Unfortunately, there's no trace of it in the ...