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

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7
votes
7answers
429 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
169 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
202 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 ...
11
votes
4answers
295 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
230 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 ...
11
votes
2answers
1k 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
338 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 ...
27
votes
12answers
1k 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 ...
5
votes
5answers
1k 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}} ...
21
votes
3answers
804 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
368 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
2k 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
334 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: ...
9
votes
1answer
189 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 ...
7
votes
3answers
506 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
174 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
164 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
227 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]]. ...
1
vote
1answer
223 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
441 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}} ...
3
votes
2answers
250 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
405 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: ...
12
votes
4answers
321 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
159 views

Behavior of Inner depends on List dimensions?

Consider the following case: ...
3
votes
1answer
158 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
357 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 ...
5
votes
2answers
266 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
411 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 ...
20
votes
5answers
722 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,... ...
12
votes
2answers
1k views

How do I split up a curve into segments 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
233 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
258 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. ...
7
votes
3answers
541 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
251 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
462 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
80 views

Need help to finish this prime signature function?

I'm trying to create a prime signature for line segments. ...
4
votes
5answers
1k 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
198 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 ...
16
votes
7answers
1k 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
711 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
305 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
159 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
412 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 ...
7
votes
2answers
1k views

Finding all partitions of a set

I'm looking for straightforward way to find all the partitions of a set. IntegerPartitions seems to provide a useful start. But then things get a bit complicated. ...
11
votes
7answers
214 views

DateList coupled with String Operations

Through some webscraping, I have the following list: ...
2
votes
3answers
222 views

Taking only particular subsets and doing calculations

I have subsets formed from a list using the Subsets command and want to do a particular calculation, lets say subtraction using the ...
3
votes
2answers
227 views

How can the lowest non-zero value in a nested list be found and its position in the sublist returned?

In the example code below we have a list of triples that produce one or more sublists with at least one zero value. How can the positions of the lowest non zero value in each sublist be returned ...
23
votes
6answers
1k views

Mathematica Destructuring

Context I'm writing a function that look something like: ...
6
votes
2answers
331 views
0
votes
2answers
253 views

Calculating average distance

I have a program that gives the average distance as the output. When I tried to repeat finding the average distance 100 times using Table, It failed to generate the output. This is the program. ...