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

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2
votes
2answers
176 views

Comparing elements of the $n^{\text{th}}$ sublist in a ragged list with the $n^{\text{th}}$ member of a sequence

I have a list of lists that are not of the same length (for example, {{6}, {14}, {6, 26, 30}}), but I have to compare every element in the $n^{\text{th}}$ sublist ...
4
votes
1answer
151 views

MapThread with several cells as output

Assume I have defined the following function: FF[{x_, y_}] := {x^2 + y^3, 3.5*x*y} I would like to apply FF on a list of ...
21
votes
8answers
758 views

Applying And to lists of Booleans

I'd like to take {True,True,False} and {True,False,False} and apply And to get ...
1
vote
1answer
112 views

How can I manipulate with elements inside sublists if sublists of different lenght?

I have some kind of output like this: {{1, 5}, {1, 13}, {1, 5, 25}}. I would like to be able to enter in each sublist and make sums of every two elements in sublists, for example my desired output ...
3
votes
2answers
100 views

How to uncompress only the compressed elements in a matrix

I have data in a rectangular structure – something like matrix={{a,b,c},{d,e,f},{g,h,i}}. The problem is that some of the columns consist of uncompressed data and ...
5
votes
6answers
345 views

Creating sums of elements from a list

I have a list $(d_1, d_2, .. d_k)$ and I want to create all sums that I get for adding only two elements for my list $(d_1+d_2, d_1+d_3,...d_{k-1}+d_k)$. The ...
14
votes
7answers
397 views

Get the first element after the first sequence of length N of consecutively increasing values

I'm looking for an efficient way of extracting the first element after the first sequence of N consecutive elements in which the values are increasing. If these are the data of a toy example: ...
7
votes
7answers
523 views

How to pick an element of a row corresponding to the minimum in a particular column?

How can I find what value in column 1 of my list corresponds to the minimum value in column 2?
3
votes
1answer
176 views

Efficiently keeping elements in a list (an input list) that exist in another list (a keep list)

I have some code that generates lists of integers (one such list is called, for example, inputList). I also have a "master list" of integers that should be kept, ...
1
vote
2answers
290 views

How to arrange a list on a triangular pattern?

I've made a multiplication table with this: Then I removed the repeated permutations with: gg = Range[1, 10]; Subsets[gg, {2}] // TableForm Now, when the ...
12
votes
4answers
375 views

Thread a function over a list and with a non-atomic 2nd parameter?

From the documentation, Thread's behavior on functions where the first parameter is a List and the second is an atomic expression, is this: ...
1
vote
2answers
264 views

Symbolically associate vectors and their norms

I am wondering how to handle the following situation: I do have vectors of known dimension that I would like to handle symbolically. I suppose I can do something like ...
20
votes
2answers
2k views

Sorting a list with secondary criterion

Is there an easy way to sort a list on multiple levels of criteria? By this I mean, first the list should be sorted according by criteria A (the same as using the usual sort function, ...
9
votes
5answers
409 views

Finding first instance of a relationship between elements in two lists

Suppose I have two lists, say: A = {1,5,10,200,50,7} B = {4,3,19,78} For each element in A, I would like to find the index of the first element in B which ...
34
votes
12answers
2k views

Map a function across a list conditionally

It seems that this is a really basic question, and I feel that the answer should be obvious to me. However, I am not seeing. Can you please help me? Thanks. Suppose I have a list of data ...
9
votes
5answers
3k views

Replace values which obey certain criteria

I'd like to replace all values in a list which obey one or more criteria with another value. Example: Replace all values>30 by 30. data={{3,35},{2,7}} ...
23
votes
3answers
1k views

Emulating R data frame getters with UpValues

What's the best way to emulate R's data frames functionality? This includes the ability to select rows and columns in a 2-dimensional table by the string identifiers positioned typically in the first ...
2
votes
4answers
435 views

Building a list recursive with one or more arguments

Consider the following: data={a,b,c,d}; res={{a,b,c,d},{b,c,d,e},{c,d,e,f},{d,e,f,g}}; The idea is to define a function ...
14
votes
6answers
3k views

Counting negative values in list

I would like to count the negative values of a list. My approach was Count[data, -_] which doesn't work. How can I tell Mathematica to count all numbers with ...
7
votes
2answers
372 views

find subsequences of constant increase

A list like l = {0, 1, 2, 3, 4, 5, 7, 9, 12, 13, 18, 19} may have subsequences of constant increase, $a_{n+1} = a_n + k$. For example: ...
11
votes
1answer
232 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 ...
10
votes
3answers
843 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 ...
3
votes
4answers
180 views

Building intervals

I'm facing the right know the problem of building intervals to an arbitrary number. The special thing is that the first and the last intervals should have fixed length, while the "middle" ones should ...
1
vote
2answers
175 views

Using patterns in ReplaceAll to extract elements from tuples at arbitrary depths

Please consider the following: I need to extract from MyList all last parts of each 3-tuple. ...
4
votes
2answers
230 views

Simpler way to repeat an execution with 2D points?

q has the coordinates of quadrilateral. I can get the output below with brute-force but I want to find a simpler solution, perhaps something like f<-q[[1;;2]]. ...
2
votes
1answer
256 views

How can I permute a multiset?

I have a multiset {1, 3, 3, 1, 2} and would like to randomly permute the classes like so: {2, 1, 1, 2, 3} or {3, 2, 2, 3, 1}, what is the simplest and most efficient way to do this? In reality the ...
7
votes
1answer
580 views

Very fast way to do a coordinate frame transform

I need a function that rotates and translates a huge amount of line segments. For example, I have a set of line segments in the form {{x0,y0,z0},{x1,y1,z1}} ...
4
votes
2answers
288 views

Creating a Nearest function programmatically

I've been trying to work out how to create a Nearest function programmatically. My goal is to produce something similar to this, a hand-assembled function: ...
-5
votes
3answers
491 views

Constructing lists by applying functions to another list

Suppose f is a function of two variables: $f = f(x,y)\quad$ and $L$ is a list. Could someone help me in defining a list of the form: $D = \{f(x,y)\ |\ x \in L,\ y \in L\}$ I tried this: ...
13
votes
4answers
378 views

The gap between MapAt and ReplacePart for 2D data tables with headers

Consider a relational table derived from survey data, where each column ("001-01" ...) represents a responder and each row (...
8
votes
2answers
170 views

Behavior of Inner depends on List dimensions?

Consider the following case: ...
3
votes
1answer
167 views

splitting a list into files

Given is a list with x, y, z coordinates: {{100, 94, -1.112}, {100.05, 94, -1.112}, {100.1, 94, -0.982}, ..., {100, 94.25, -1.112}, {100.05, 94.25, -0.855}, {100.1, 94.25, -0.728}, ..., ...
10
votes
3answers
465 views

Generating Linear Extensions of a Partial Order

Given a set $S$ and a partial order $\prec$ over $S$, I'm looking for a way to "efficiently" generate a list of linear extensions of $\prec$. Suppose the partial order is given by a ...
6
votes
2answers
402 views

Creating a list of PopupMenus that dynamically update an element in a list

So as the title says I am trying to make a list where each element is determined by a users choice of an element in a PopupMenu. My first attempt: ...
1
vote
1answer
453 views

Fastest way to sum pairwise potentials

I've been writing a function to sum a pairwise potential on two lists, i.e. two charged bodies, each containing N >> 1 and ...
21
votes
5answers
870 views

MapThread over sublists of different length

I have a list which looks like this: l={{1,0,3,4},{0,2},{0,0,1,3},{1,2,0}}. Now I would like to count how many 0s the sublists contain in the first, second,... ...
16
votes
2answers
2k views

How do I split up a curve into chords of equal length?

I have a curve that is defined as f[x] and what I'm attempting to do is to divide the curve into equal straight lengths for a number of segments of my choosing that I've defined as nSeg. I've created ...
3
votes
2answers
258 views

Using the elements of a subset in a Do loop

I would like to use the elements of Subsets in a Do loop. I have: ...
3
votes
3answers
366 views

Incrementing a nested list element

I've been wanting to increment a nested list element of which I know the "coordinates". I thought of the following procedure, using Apply with Part. ...
12
votes
3answers
837 views

Specifying string patterns in DeleteCases

It seems that DeleteCases is not compatible with string patterns, at least directly (see, for example, this question). Is this true? If so, why is this the case? ...
4
votes
2answers
279 views

Access pairs of vectors, rather than the matrices, in partitioned data structure at a levelspec

I have some old code to analyze correlation between 2 time series by looking at windows of different lengths shifting across the time series data. The code: gets 2 sets of time series data (in ...
5
votes
3answers
890 views

position of sequence of elements in list [duplicate]

Possible Duplicate: Finding a subsequence in a list Question The position of {3, 5} is the list {1, 3, 4, 3, 5, 5, 1} is 3. How can such a position ...
0
votes
1answer
87 views

Need help to finish this prime signature function?

I'm trying to create a prime signature for line segments. ...
4
votes
5answers
2k views

Dealing with Empty Brackets in a List

I have a large list with varying constituent parts. Some of these are like this: i.e. graphlist[[34]] ...
7
votes
1answer
238 views

Built in way to de-list singletons?

Is there a built in method to de-list singleton expressions, like this rule-based solution: expr_ :> If[Length[expr] == 1, First@expr, expr] In data ...
17
votes
7answers
2k views

How do I check if any element in a list is positive?

As a simple example of what I would like to do, suppose I have a list a of all real numbers. I would like to perform a simple check to see if some element of ...
0
votes
2answers
1k views

How to generate table without comma and bracket or get rid of those?

I want just data without comma and brackets. Even TableForm is not working for me. For example, the general pattern of my table is ...
3
votes
5answers
361 views

How to extract strings from the list with an additional condition on previous elements?

There are a long list of strings $s$ and two lists of substrings $s1$ and $s2$. I want to take all elements of $s$ which contain a substring from $s2$ and such that before it on no more than $n$ ...
3
votes
3answers
217 views

Function[] argument nesting for operations like Select[]

The following code selects a special element from a list thelist = {"this", "notthis"}; Select[thelist, (# == "this") &] What I want is a function which ...
5
votes
3answers
589 views

Adding Lists Together

This is something that should be simple, but the documentation and other questions don't seem to deal with it. I can think of mechanically doing it through a loop, but I know there must be a better ...