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

learn more… | top users | synonyms (3)

10
votes
2answers
304 views

Using Gather to rearrange my data

I have a list of elements: {{1, 2}, {1, 5}, {2, 6}, {3, 7}, {4, 8}, {5, 6}, {5, 9}, {9, 13}, {10,11}, {11, 12}, {11, 15}, {15, 16}} I have to divide it into ...
10
votes
1answer
613 views

Modifying a List in a function in place [duplicate]

An example will be most specific: func[list_, column_] := list[[All, column]] = Map[#*2 &, list[[All, column]]]; This throws errors. I want to avoid doing ...
8
votes
7answers
684 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
5answers
369 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. ...
7
votes
2answers
351 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: ...
6
votes
1answer
458 views

Count sublists which match pattern

I have a list which looks like this: data={{12,0},{0,0},{20,1},{0,0}, {0,-1}}. Now I would like to count the number of sublists which: have both slots zero the ...
6
votes
3answers
664 views

Subsets of a list

Consider the following demand of products for the next four months. data={1,20,3,40}; I could produce the whole demand in the first months, leading to the ...
4
votes
4answers
411 views

Listing matrices up to symmetry

I am interested in the equivalence relation on N x N binary matrices, in which two matrices are equivalent if one can be obtained by rotating/reflecting the other. I would like to obtain a list ...
1
vote
2answers
437 views

Specifying parts from lists for plotting using Show

I have the following data: ...
0
votes
1answer
3k views

Table - find index of the maximum element [duplicate]

Let's suppose that I have table t = {1.23, 3.4, 10, 34, 1.78, 0.98, 12.56}. To take the biggest element I can use Max[t] ...
10
votes
4answers
326 views

MapThread with non-rectangular lists

MapThread works fine and dandy with rectangular list structures: MapThread[f, {{{a, b}, {c, d}}, {{1, 2}, {3, 4}}}, 2] ...
9
votes
5answers
342 views

How can I remove matching sublists from my list?

I want to use DeleteCases (or any appropriate function) to remove elements of a list, which in turn are lists of fixed size. The rule I wish to apply is that any ...
8
votes
3answers
297 views

Generalization to AllTrue, AnyTrue and NoneTrue

I am wondering if there is a natural Mathematica way to generalize those functions. To be specific, All three functions AllTrue, ...
8
votes
4answers
316 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
2answers
365 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
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... ...
7
votes
6answers
200 views

How to join held Lists?

Let's say I have a = Hold@{2+2} b = Hold@{4+4} How can I get Hold@{2+2,4+4} ie join the two held lists ? More ...
7
votes
2answers
246 views

Programatically adding/retaining comments within a nested list

Is it possible to convert the following list of strings to computable numbers with the comments preserved? ...
6
votes
2answers
348 views

Finding the coefficient of a certain power in a generating function

I want to compute $(t^1+\dots +t^5)(t^2+\dots+ t^6)(t^3+\dots +t^9)$ and find the coefficient of $t^{15}$ for example. $t$ is an indeterminate Now in Maple this is simply as ...
6
votes
2answers
334 views

How can I find if the number of subsets for a list is very large?

I'm trying to find the following; Subsets[Range[2, 2300], {4}] but my computer gave the following error: ...
5
votes
1answer
381 views

Apply color function to matrix plot

I want to apply the following color rules to a large table of numbers. I have extracted a part of the table to use as an example. I would like to assign 5 different colors to 5 different ranges of ...
5
votes
2answers
503 views

How to combine elements of two matrices?

Given two matrices m1 and m2, e.g.: m1 = {{a1, b1}, {c1, d1}} m2 = {{a2, b2}, {c2, d2}} How can one obtain the following? ...
5
votes
1answer
436 views

Using Partition to allow sublists of different lengths

As a minimal example, suppose I have a list of the integers from 1 to 25. Suppose I want to use Partition to partition the list into sublists of length 10 but ...
5
votes
4answers
422 views

Leveling peaks in list

Consider the following: data={2,2,2,5,3,3,3,6,1,1,1,0}; In[1]:=result=MyFunction@data Out[1]:={2,2,3.5,3.5,3,3,4.5,4.5,1,1,1,0} ...
4
votes
1answer
498 views

Why is there a huge performance gap using Map with more than 100 List entries

im using Map on a List like this: cube= {{1, 1, 1}, {1, 1, 2}, {1, 1, 3}, {1, 1, 4}, ... , {5, 5, 4}, {5, 5, 5}} Mapping the whole List with 125 entries takes ...
4
votes
4answers
261 views

Elegant Matrix Combinations

Suppose you have a matrix (mxn), simplified for illustration m= {{a, b, c}, {d, e, f}} And a set of combinations (simplified for illustration purposes but can ...
4
votes
2answers
176 views

Multiplying expressions within a list of pure functions

Let's say I have a list of pure functions that are nice algebraic expressions: say l = {(#1 - 1)&, (#1^2 + #1)&, (#1^3 - 1)&} What's an easy way to ...
3
votes
0answers
98 views

Gather dependency on list order?

I get intrigued about Gather behavior on this post. I thought that Gather was invariant under list order? Here is the result I ...
3
votes
2answers
2k views

Calculating the distance between the coordinates in a list

I have a list of coordinates {{A[9, 4, 7], 0.0395174}, {A[1, 5, 0], 0.0163797}, {A[0, 7, 2], 0.0577425}, {A[2, 7, 5], 1.01313}} I want to find the distance ...
2
votes
4answers
819 views

ListPlot multiple datasets over same x-values

Is there a better way to enter my data into a list plot? ...
2
votes
1answer
233 views

Extracting information from list

I have a huge list that looks like this: ...
2
votes
1answer
435 views

RowReduce: Solving for the resource vector (a, b, c) in Augmented Matrix

Here are two examples: RowReduce[{{3, 1, a}, {2, 1, b}}] evaluates to {{1, 0, a - b}, {0, 1, -2 a + 3 b}} but ...
1
vote
3answers
156 views

Binning events with weights

I have two vectors, one containing sampled energies and the other one for each of these energies a weight: e(i) and w(i). I ...
1
vote
2answers
248 views

How to blend some colors on a curve

I need to define a color gradient on a 3D curve, but I'm having some problems with this. Suppose we have a 3D curve defined as a parametric function of some real variable ...
1
vote
1answer
219 views

Syntax for integrating over limits specified by a Table

I wish to use NIntegrate to compute multidimensional integrals. However, I don't want to manually input the limits for the dimensions. I want to store the ...
17
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, ...
11
votes
2answers
359 views

Conditional Gathering of lists

Just need a little help with the GatherBy / SplitBy function(s). I have a list of random numbers here: ...
7
votes
1answer
403 views
7
votes
4answers
232 views

Button's command is not evaluated in iteration

I wish I didn't feel like a newbie after several months, but... If I enter the following: Table[ Button[ "Number: " <> ToString @ i, Print @ i], {i, 1, 5}] ...
6
votes
8answers
316 views

Merging lists and adding common elements [duplicate]

I have two 2D arrays where some of the x-values are identical, L={{1,1},{2,2},{3,3}}; J={{0,1},{2,2},{4,4}}; I want to add these lists in the following way ...
6
votes
6answers
420 views

How can I merge two lists in a special way?

It's been over a year since I've used Mathematica, and I'm having a total brain fart on a home project. I'd like to take an existing list of lists, say, ...
5
votes
2answers
243 views

Better method for creating a tuple out of two lists

I just combined two lists using this method ...
5
votes
2answers
500 views

Add elements in a sublist

I have created a subset of arrays: ...
4
votes
8answers
421 views

How to sort my list?

For example I have two lists of such structure L1 = {{"Australia",a1}, {"USA",a2}, {"Norway",a3},...} L2 = {{"Russia",b1}, {"Norway",b2}, {"Japan",b3},...} I ...
4
votes
2answers
210 views

Correlation with missing data

I have two lists, age and score, that I want to find correlation on for 50 people. For some people, the score is blank. Example data: ...
4
votes
5answers
1k views

Removing zero values from ordered pairs

I have some processed data, which are basically a collection of ordered pairs in the form: {{x1, y1}, {x2, y2}, ..., {xn, yn}} Ordered pairs which have either a ...
4
votes
1answer
319 views

Path queries for tree-structured data

Can anyone suggest documentation or tutorials for developing path queries and indices for (XML-like) tree-structured data? Suppose data is organized hierarchically in key->value pairs, eg: ...
3
votes
1answer
427 views

Select row from a table by column value [duplicate]

I have the following: animals = {{dog, black, 200}, {cat, white, 100}, {moose, brown, 500}, {zebra,black,100}} If this came from a SQL table called animals, ...
3
votes
4answers
529 views

More elegant way

I read ReplaceOrRemoveInvalidOrMissingData Mathematica documentation, and I tried to apply the same approach to my dataset. I've got two problems, but one is only a style problem! There is one more ...
3
votes
7answers
369 views

Concise way to generate multiset lists

I wrote the following to generate a multiset with the same number of items over a fixed range: ConstantArray[#, 3]& /@ Range[9] // Flatten ...