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

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10
votes
6answers
582 views

How to Map a subset of list elements to a function?

How would you, given a list {1, 2, 3, 4}, apply a function f to 1 and ...
9
votes
5answers
520 views

Counting the population of integers

Suppose that myData is a list of sublists. Each sublist has a length of one or greater and contains any number of replicates of the integers 1, 2, 3, and 4. I ...
35
votes
8answers
2k views

Levels: how do they work?

I cannot understand how Mathematica manages levels, and so it's always a painful try-and-fail to use Flatten. Can someone please give me a very clear definition? ...
35
votes
3answers
1k views

Tiling a square

I wondered if there was a way to automate the process of finding a way to tile a tile into a square. The idea is to represent the tile with a matrix of $0$s for blank space and $1$s for filled spaces ...
22
votes
3answers
486 views

Undocumented form for Extract

Prompted by a comments conversation here, here's an interesting (and often performance enhancing) use of Extract: ...
18
votes
4answers
591 views

Accessing list elements by name

First, a bit of a long introduction to my problem: I only have a few weeks of Mathematica experience. I am creating a mathematica application that calculates some material properties of steel based ...
17
votes
5answers
600 views

Map-Thread-Through-Apply a list of functions onto a list of (lists of) values

I have a list of functions: fns = {f, g, h} and a list of triples: ...
12
votes
7answers
862 views

How to Set parts of indexed lists?

I would like to assign a list to an indexed variable and then change it using Part and Set like this: ...
18
votes
8answers
1k views

Selectively Mapping over elements in a List

I am using the following code to easily generate a row of images of all eight planets of our Solar System: ...
14
votes
4answers
570 views

Implementing a function which generalizes the merging step in merge sort

One of the key steps in merge sort is the merging step. Given two sorted lists sorted1={2,6,10,13,16,17,19}; sorted2={1,3,4,5,7,8,9,11,12,14,15,18,20}; of ...
21
votes
11answers
540 views

Using MapAt to map at a particular depth (levelspec)

I have the following sample list (my actual list is, of course, much longer): ...
15
votes
6answers
1k views

Best way to extract values from a list of rules?

Mathematica has a lot of list manipulation functions, and, also because I don't work with lists often, at times I'm a bit lost. I'll find a way, but I'm sure it's not the most efficient. Case in ...
11
votes
3answers
513 views

Simpler way to fill date gaps with zero values

One basic problem when working with data like sales and dates is the case where you dont't have sales in all days, so you have to fill it to take information as average or to make a plot. See this toy ...
5
votes
3answers
3k views

Local max/min of Mathematica data sets

Is there a way in Mathematica to find the local maxima of a set of points? Suppose you have ...
10
votes
1answer
1k views

Finding a subsequence in a list

I have a list and I want to find (in this particular case the first) appearance of a any of some subsequences, of possible different lengths. None of the subsequences is a subsequence of each other. ...
7
votes
2answers
1k views

Get the coordinates from ContourPlot and RegionPlot

How do I get the coordinates from a contour plot I've done in Mathematica? For example, I have a two-variable function f[x, y], for which I can make a contour plot: ...
1
vote
4answers
373 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 ...
14
votes
7answers
1k views

Selecting a sublist based on Length

If you have a simple list of lists as follows: test = {{1, 2}, {4, 5, 6, 7}, {5, 4, 3}} How do you ask Mathematica to return the sublist of greatest length? ...
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. ...
1
vote
3answers
991 views

How to create functions of arbitrary number of variables? [duplicate]

In the following code what would be the simplest way to generalize it to say some $N_f$ number of $z$ instead of just $z_1$ and $z_2$? ...
16
votes
3answers
3k views

K-means clustering

In MATLAB, there is a command kmeans() that divides an array into $k$ clusters and calculates the centroid of each cluster. Is there any command in Mathematica to ...
19
votes
3answers
595 views

DeleteDuplicatesBy is not performing as I'd hoped. Am I missing something?

Déjà vu: a new-in-v10 function should provide a better solution to an old problem, but my enthusiasm is curbed when I run timings. This time the function is ...
11
votes
2answers
1k views

Simple algorithm to find cycles in edge list

I have the edge list of an undirected graph which consists of disjoint "cycles" only. Example: {{1, 2}, {2, 3}, {3, 4}, {4, 1}, {5, 6}, {6, 7}, {7, 5}} Each ...
14
votes
5answers
1k views

From a list to a list of rules

Starting from these two lists, var = {a, b, c} values = {{1, 2, 3}, {4, 5, 6}, {7, 8 , 9}} how can I generate a list of rules? ...
8
votes
3answers
643 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 ...
14
votes
4answers
429 views

“Unflattening” a list

Imagine we have a list with some hierarchical structure: list = {{{2,3},{2,4}},{{{3,4}}},{{5,6},{7,8}}}; Which we then flatten to some level in order to process ...
11
votes
2answers
790 views

How do I find the elements in a list that return the highest value for a function?

Suppose we have a list of values and a function f. I want to find which of the elements maximizes the return value of the function in Mathematica. Let call the ...
7
votes
3answers
252 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 ...
5
votes
2answers
491 views

Finding the intersection of two date lists

I've got two lists that look like this ...
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 ...
12
votes
4answers
297 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 (...
7
votes
4answers
439 views

Find list position and mapping list

Sorry, my English is not very good. I have two lists: ...
7
votes
4answers
476 views

Prepend 0 to sublists

My question is similar to this one, but my goal is to prepend a single 0 the each sublist, not incrementally many 0's. The file I'm working is a CSV containing around 50K sublists of length 35. I've ...
6
votes
3answers
169 views

How to 'merge' a list like FromDigits, but with a mixture of numbers and symbols?

How do I go from {C,4,G,5,S,7} to C4G5S7
6
votes
5answers
389 views

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

I have a list of pairs, for example: ...
15
votes
6answers
1k views

Max of a table/list with indeterminate values

Suppose I have a Table: tab = {1., 2., 3., Indeterminate} When I type Max[tab] I get ...
7
votes
3answers
214 views

How to Flatten Array of Arrays of the highest order in a simple way?

I have a matrix of matrices, given in the following code. I want to flatten the array... ...
6
votes
4answers
252 views

How to sum over duplicates?

I have a list of the form: {{1, 0, 1}, {2, 1, 2}, {1, 0, 3}, {2, 4, 2}, {2, 1, -1}, {1, 0 ,0}} that I would like to sort such that I calculate the sum over the ...
5
votes
5answers
404 views

Elementwise join

I have two tensors of arbitrary but equal rank n (and equal dimensions): A and B, and I want to get a third tensor of rank n + ...
5
votes
2answers
508 views

How can I get every distinct size-n combination of a list?

Let's say I have a list: {a, b, c} I would like to, for say $n=2$ get every distinct pair from that list. That is, the expected result should be, for some ...
5
votes
5answers
524 views

Prevent Part[] from trying to extract parts of symbolic expressions

If you have a list, e.g. {1, 2, 3} then you can extract the $k$th part using Part (...
2
votes
3answers
255 views

Re-arranging / selecting of a data table very slow in For loop [duplicate]

My task is quite simple; I have a table of data like M = {{1,2}, {1,3}, {3,4}, {5,1}, {6,9}, {6,8}, {6,1}}; so the table is sorted with respect to the first ...
12
votes
2answers
922 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 ...
19
votes
2answers
640 views

Data Table Manipulation in Mathematica: Step 2

In this previous post (Data Table Manipulation in Mathematica) we find the brilliant suggestion proposed by Leonid Shifrin that allows to select specific rows identified by the header name. I'm now ...
14
votes
9answers
474 views

Distributing elements across a list of lists

I have two lists: u = {{1, 3}, {2, 6}, {3, 9}} v = {0, 4} and I want to obtain this list from them: ...
20
votes
7answers
1k views

How to Derive Tuples Without Replacement

Given a couple of lists like a={1,2,3,4,6} and b={2,3,4,6,9} I can use the built-in Mathematica symbol ...
13
votes
6answers
895 views

Splitting up delimited data in lists

One task that I frequently find myself doing in Mathematica is splitting lists into lists of sublists, using specific elements to define the break-points. This is particularly useful with imported ...
10
votes
4answers
293 views

How to pass a list of arguments into HoldAll

I have a list of arguments (which in reality is lengthy): arguments = {a, b, c} arguments2 = {a_, b_, c_} f[Sequence@@arguments2] := a + b + c Note: It seems ...
10
votes
1answer
512 views

How to monitor the progress of Map?

I have a function doSomethingComplicated[...] that takes about 10s on average to evaluate. My list, listOfArgs has about 10000 ...
8
votes
1answer
159 views

Quickly selecting for points in a set that are within a critical distance of points in another set

Imagine two lists of two-dimensional coordinates: listA = RandomReal[{0,100},{202,2}]; listB = RandomReal[{0,100},{97,2}]; I'm attempting to quickly generate a ...