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

learn more… | top users | synonyms (3)

10
votes
3answers
431 views

Zero-dimensional matrices

In a recent Mathematica project, $(n \times 0)$- and $(0 \times n)$-dimensional matrices have suddenly become a frustratingly common edge case for me. For instance, consider the following two ...
10
votes
3answers
245 views

Can I return lists with different dimensions from a compiled function?

Sometimes I'll need several lists with different dimensions to be returned by a compiled function, but compiled function will fail if an irregular list contained: ...
4
votes
4answers
332 views

Deleting powers of a common prime except the highest one from a list with further only primes

In a list with factors of which most are prime, some are integer powers of some common prime as base. All the powers from 1 to ...
0
votes
2answers
249 views

Replace all elements of a list

I have a set that looks like: s = {{1, 2, 3} -> 9, {4, 1, 9} -> 9, {3, 7, 3} -> 1}; Now, I want to replace each element of the set by the lhs of "...
5
votes
1answer
182 views

MapThread over large graph

I am trying to build a very large graph with approximately $16\,000\,000$ edges, each being a two-dimensional integer vector. I have a list of edges in the form $\{\{e_{11}, e_{12}\}, \{e_{21}, ...
1
vote
2answers
210 views

Deleting parts from a nested list

I have a very long nested list. Here is a short example: list = {{1.2, {1, 1, 1, 1}, {2, 2, 2}}, {0.9, {3, 3, 3, 3}, {4, 4, 4}}, {1.4, {4, 4, 4, 4}, {5, 5, 5}}} ...
12
votes
6answers
647 views

Elegantly split a matrix into positive and negative parts?

I have a matrix $M$ of real components, and I want to split it into two matrices $M^+$ and $M^-$ of the same dimensions as $M$, where $M^+$ contains the positive components of $M$ (the remaining ...
2
votes
1answer
710 views

Calculate mean square displacements for different particles from a excel file

I have the particle movement data in the following format: ...
2
votes
3answers
142 views

How to do subtraction with sets in which the elements have multiplicity indicators? [duplicate]

I want to do subtraction with sets l1 and l2, which contain multiplicity indicators. For example, ...
6
votes
3answers
247 views

Loop function over list [duplicate]

I would like to divide element 1 of a list by element 2; element 2 by element 3, and so on. What is the best way of doing this? I have tried f = #1/#2 & ...
1
vote
1answer
168 views

How should I go about writing more functional and list based code? [duplicate]

I've heard that Mathematica is usually faster when the code is list-based and/or uses a functional paradigm. I'm still working on getting the hang of this; there are a lot of ...
2
votes
2answers
128 views

Deleting elements on a list by the first element of another list

I was trying to make this L1 = {{2, 1}, {6, 4}, {8, 7}, {9, 5}}; L2 = {{2, 9}, {9, 6}}; L = Union[L2 , L1] And I used this: ...
6
votes
3answers
372 views

Mapping a function that assigns values to a list over a different list

I'm trying to get used to Mathematica's approach to programming and list manipulation, and am struggling with one thing. Say that I have a function f which takes a ...
0
votes
2answers
108 views

Code for sum of exponential divisors function

Consider $n = p_{1}^{a_1}\cdots p_{r}^{a_{r}}$. An integer $d = p_{i}^{b_{i}} \cdots p_{r}^{b^{r}}$ is called an exponential divisor of $n$ if $b_{i}$ divides $a_{i}$ for every $1\leq i \leq r.$ I am ...
1
vote
1answer
114 views

How to apply compiled function on list

Compile function output error: How to apply compiled function on list? ...
2
votes
1answer
85 views

Convert Integer to Numeric with Replacement rules

I have a long list of triples, each looking something like {AGO, 1988, 2345.23}. Some of these, however, have an integer in the third spot, like this: ...
1
vote
0answers
215 views

Using Part within a Compiled Command

I'm looking to define a multi-line function that makes use of the "Part" command. A toy example: ...
1
vote
0answers
69 views

Produce {f[x],g[y],h[z]} in as many ways as possible [duplicate]

I have two lists of equal lengths but for my task I will use 3-element lists , namely {x,y,z} and {f,g,h}. The first contains ...
1
vote
2answers
158 views

Add a column to a matrix as a function of the other columns

I was wondering if its possible to add a column to a matrix by a formula that uses all other columns, like this: ...
0
votes
3answers
885 views

Find the number of nonzero elements

How do you find the number of elements in a matrix that are non-zero. For instance, the following matrix has 5 nonzero elements. ...
0
votes
1answer
222 views

Performing matrix multiplications with a list

I have a question in regards to PseudoInverse. I have $A$, an $n\times 2$ matrix, and when I want to compute $(A^T A)^{-1}A$, by using ...
6
votes
2answers
124 views

Get brief help for a set of functions

When we are in console mode or working with a notebook we can get brief help about a function just by shift-entering ?function I would like to have a list like ...
4
votes
2answers
4k views

How to combine two vectors into a matrix by columns?

I know it may sounds idiot, but I've been looking through the document, and couldn't find a way to combine two vectors say {a, b} and ...
3
votes
3answers
380 views

efficient way to give nearest neighbour and next nearest neighbour of every point in a point set

Suppose we have a point set, the points are labeled 1,2,3,....n. And p[i] is the coordinate of the point. Now I want the label of nearest and next nearest point ...
0
votes
0answers
43 views

Store results of inequality [duplicate]

I eveluated some values using Reduce commend and I store them in a Table ...
8
votes
7answers
790 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 ...
18
votes
9answers
1k views

How to replace an element in a list based on the value of the next element?

I use Mathematica a little bit. I try to understand it, but it is hard I have a list of 5 numbers selected randomly from 0 and -1. I have to replace a 0 with a 1 when the 0 is followed by -1. My ...
4
votes
1answer
185 views

Efficient ways to rotate a ListPlot?

I have a numerical solution from a differential equation that is in the form of a list, in $(x,z)$-plane. I would like to rotate the 2D ListPlot around the $z$-axis ...
11
votes
10answers
536 views

How to pick increasing numbers from the list

How to pick increasing numbers from the list. lst = {5, 3, 6, 2, 7, 4, 8}; out: {5,6,7,8} So many interesting ...
5
votes
6answers
302 views

Convert array from {{…}} to “[[…]]”

I have made this function: conv01 = Map["["<>StringJoin@@Riffle[#,","]<>"]"&,Map[ToString,#,{2}],{0,1}]& to convert: ...
0
votes
1answer
110 views

How to create 2k sized vector in k sized loop

I want to solve a system of simple differential equations. At some point I need to solve non-linear system of algebraic equations with Newton method. I would like to efficiently create a right hand ...
6
votes
2answers
197 views

how recover lost data of coordinates from contourplot of mention data?

I have made Contour Plot for a lot of data, like this ...
1
vote
2answers
112 views

How to return matching sublists or empty list

How to return matching sublists or empty list m1 = {{1, 0.5}, {2, 0.4}, {3, 0.1}}; m2 = {{1, 0.5}, {0, 0.4}, {0, 0.1}}; Commonest[Join[m1, m2]] out: ...
2
votes
2answers
171 views

Organise data in table

I have a large amount of data available (in excel), which is not very organised. I can do this by copy paste, but I am trying to do this using mathematica. Hopefully someone can help me. I imported ...
-2
votes
1answer
84 views

Using Product for different variables

when using product in mathematica the initial and maximum value of the product will be the variable itself that will be maupulated. what I need is to make these initial and maximum of the product as ...
3
votes
2answers
622 views

How can I scale the y axis?

I have a file I import and read into a table of $2 \times n$. I can plot this data using the following code: ...
1
vote
3answers
215 views

Code hanging inside a For loop

I'm pretty new to Mathematica (and functional programming in general). I'm working on some code to find winners (maximal values) in a list. The code I have that is hanging is this line. ...
4
votes
2answers
144 views

Coordinates for multiple countries

I am trying to plot polygons for multiple countries, say "UnitedStates" and "Canada". US data is generated thus: ...
8
votes
8answers
443 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 ...
16
votes
2answers
3k views

Is there an equivalent to MATLAB's linspace? [duplicate]

Does Mathematica have an equivalent to Matlab's linspace? I want to make a list with "start", "stop" and "number of points". What is the neatest way of doing this?
3
votes
6answers
307 views

Compute ratios of elements in two lists

I have two lists, say a and b, both of length n. I'd like to compute the following: ...
2
votes
2answers
84 views

How can I generate a variable-length list of options in PieChart?

I would like to allow a user to manipulate the segments of a pie-chart, which is to be generated from a list of a specific format. The code looks something like the following: ...
11
votes
4answers
780 views

List comprehension in Mathematica

Python supports a concept called "list comprehensions". Following is sample example ...
13
votes
11answers
971 views

How to get list of duplicates when using DeleteDuplicates?

This might be easy, but can't find a way to use DeleteDuplicates to get also list of the actual duplicates. Example: ...
0
votes
0answers
65 views

How to delete duplicated sublist [duplicate]

I have a list like this: ...
-1
votes
2answers
231 views

How can I extract when a select condition is met in a do loop the value of the iterator?

I use the following code to find out the number of consecutive prime numbers using a formula $n^2+n+i$ found out by Euler (starting from n=0): ...
5
votes
5answers
199 views

Reversing every second “row” in a list

I have a list that is obtained by flattening a matrix list=Flatten[Table[{i, j}, {i, 1, 4}, {j, 2, 6, 2}], 1] {{1, 2}, {1, 4}, {1, 6}, {2, 2}, {2, 4}, {2, 6}, ...
12
votes
4answers
372 views

How to enumerate all possible binary associations?

Suppose I have a list of symbols like: {a,b,c,d} I would like to enumerate all possible binary associations (combining symbols and/or sublists pairwise): ...
0
votes
3answers
104 views

List of squareful, cubeful, etc. numbers

The following works: ...
4
votes
2answers
123 views

How to constrain the generation of all possible orderings?

Here is code from Simon Woods' answer for getting all possible weak (equal ranks allowed) orderings for $N=3$ objects: ...