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

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1
vote
3answers
2k views

Loop through a list and select elements

I am new to Mathematica and I have no idea how to make a basic for loop work. I want to loop through the elements of a list: Range[45, 200]. I want to select the ...
3
votes
5answers
544 views

How to combine some elements of a list?

In order to simplify my expression, I face a list manipulation problem. For example, given the input list ...
2
votes
3answers
598 views

Selecting subsets of a list containing a specific element

I'm trying to generate all the subsets of a set containing a specific element. For example, for the set {1, 2, 3, 4}, with the specific element I want inside each subset being 4, the required answer ...
4
votes
5answers
140 views

Convert a list with three arguments {x0,x1, step} into an equidistant table?

How can I convert a list such as: a = {1, 2, 0.1} into sequence so that I can pass them into a function, e.g. I want to be able to do something like this ...
8
votes
3answers
526 views

Multiply a list of matrices by a list of vectors

How does one multiply a list of matrices by a list of vectors, elementwise? For example, multiplying ...
3
votes
2answers
171 views

Sequence and boolean And

I'm trying to figure out if a calculation result it's a valid result. As it return a matrix, I need to test that every element it's a number, so I thought this could work... ...
9
votes
1answer
232 views

Creating a number based on given conditions

In the grade 7 math curriculum here in Alberta we teach divisibility. I'm trying to write a program to create questions based on the idea of a student being given say, 4 digits, and then choosing ...
9
votes
4answers
545 views

Find list position and mapping list

Sorry, my English is not very good. I have two lists: ...
9
votes
2answers
350 views

Speed up 4D matrix/array generation

I have to fill a 4D array, whose entries are $\mathrm{sinc}\left[j(a-b)^2+j(c-d)^2-\phi\right]$ for a fixed value of $\phi$ (normally -15) and a fixed value of $j$ (normally about 0.00005). The way ...
7
votes
3answers
156 views

Given a list of lists, build a list in which lists with equal first and last elements are grouped together

I have a list of lists, and I'd like to build a new list, in which lists are in the same list if they have the same first and last element. Here's an example. Suppose I have ...
0
votes
1answer
124 views

Where do those nulls come from? [closed]

I have seen discussions of unwanted nulls in the output in the context of building lists with conditions on the elements, but that is not involved here. I would like to know where the nulls come from ...
3
votes
1answer
164 views

How to make a simple tree yourself with defined distances for each generation?

I'm trying to make a function that generates a tree for spin spin analysis in spectroscopy. I though it would be pretty easy, but I'm totally stocked. The tree should look something like this: ...
4
votes
2answers
269 views

Partition a set into $k$ non-empty subsets

The Stirling number of the second kind is the number of ways to partition a set of $n$ objects into $k$ non-empty subsets. In Mathematica, this is implemented as ...
3
votes
3answers
644 views

Sum of Multinomial Coefficients

Basically, I want to write a function to compute the following sum $f(m,L):=\sum_{0\leq k_1,\cdots, k_n\leq m} \binom{m}{k_1,k_2,\cdots k_n}$ and $\mathrm{supp}(k)=L \subseteq \left \{ 1,...,n \right ...
10
votes
5answers
531 views

Best way to modify values in a list of rules?

Recently I had to solve a problem similar to this: Let's say I have a list of list of rules ...
2
votes
1answer
114 views

Strange behaviour of variables in Table

I'm trying to work with some vectors and have run into a strange problem. An obvious way to define a difference of two vectors would be dif[x_,y_] := x-y I ...
8
votes
2answers
426 views

Finding all points of period n in an iterated map

I'm trying to implement an algorithm of Jenkinson and Pollicott to calculate the Hausdorff dimension of a Julia set for the map $f_c : z\mapsto z^2 + c$. It's described on page 40 of their paper, ...
9
votes
4answers
948 views

Passing large list by reference

I have the following problem: I would like to control evaluation of a variable that points to a list. For example, frequently in the code I have functions of the form that are supposed to work on ...
0
votes
1answer
645 views

Find Roots in Do loop

Task: Finding roots in loop t = List[1, 2, 3, 4, 5] fx[x_] := a*x^2 - 5 List[Do[Print[FindRoot[fx[k] == 1, {a, 1}]], {k, 0, 5}]] Output: Currently the output is ...
3
votes
2answers
274 views

Listable compiled function using Map

I'm trying to minimize the computation time of problem which is too long to post. I use compilein order to gain some speed. To increase speed I would like to use ...
0
votes
3answers
326 views

Finding an index with certain conditions

EDIT: I need to find out an index i which depends on certain conditions and I'm not able to implement it. I have a list (time points) $t_i$ and two constants $a,c$ ...
9
votes
5answers
571 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 ...
0
votes
0answers
64 views

get while loop output into a list [duplicate]

I would like to get the output from this while loop and use it as a list so I can count the frequency of the various tuples.. ...
0
votes
2answers
359 views

Converting a list of replacement rules into a list of real values [duplicate]

The following command outputs a list of replacement rules. ...
14
votes
3answers
421 views

Quick multiple selections from a list

What is the fastest way to make multiple selections from a list? Compiled methods included. For example, here are two methods for selecting a subset, compared:- ...
2
votes
2answers
466 views

Replacing values of a function

I have recently starting using Mathematica and have recently come to what seems as an impasse in my understanding of the language. If this is too "tell me how to do it" I would certainly understand. ...
9
votes
5answers
356 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 ...
6
votes
3answers
396 views

Delete elements from a list really fast

I have this bit of code that works, but it's very slow when there are 600k elements in the list: ...
0
votes
1answer
164 views

Discrete 3D plots of median ratios of two 2D matrices of lists of values

Lets say I have 2 2D arrays where each cell contains a list of values: Example: ...
5
votes
2answers
1k views

How do I find the Euclidean distance between one point and all the points in a list?

I want to find the Euclidean distance between one point (x1) and a list of points (y1), which contains a lot of coordinates x1 = killer[[2]] {6.05102, ...
7
votes
2answers
949 views

Elegant way to handle columns operations

Inspired by this question from @sjdh and by my recurrent use of columns operations in database sets, I was looking for one way to make columns operations more symetric, so I can handle with matrix and ...
3
votes
3answers
187 views

Count items in a list that occur before a date

I have a list of dates that happen throughout 2013. I wish to construct a graph showing a cumulative total of elements that happen before that date. I have a working algorithm, but it seems too slow ...
10
votes
4answers
650 views

How to rebuild original data from a histogram?

I have data in the following form. I have a list of values and a list of frequencies that indicate how often each value has occurred. Example list of values: ...
11
votes
2answers
653 views

Vlookup function as Excel in Mathematica

How can we create a Vlookup function, similar to what we have in Excel? So if we have a table a and another b, we could add ...
3
votes
1answer
232 views

Efficiently finding the maximum value of a column in a matrix

Imagine I have a matrix of the following form: TestArray = $((a_1,b_1,...),(a_2,b_2,...),(a_3,b_3,...),...)$, where a specific example might be: TestArray = ...
2
votes
1answer
156 views

writing a function using multiple variables

I am fairly new to Mathematica and am trying to write a function for the equation: xx = [x/(Sqrt[h^2 + d^2 + y^2]))*(Sqrt[h^2 + (d + yy)^2]) where h, d are known ...
1
vote
1answer
295 views

Frequency of elements in a list (merging tally data) [duplicate]

I've got a list in the format of list={{a,1},{a,1},{b,1},{c,1},{b,1}} And I want it to "compress" into a list of pairs ...
4
votes
2answers
250 views

How can I eliminate equivalent equations from a list?

I want to find the numbers $a$, $b$, $c$, $d$ of the plane $ax + by +cz +d = 0$ which make the distance from the point $M(1,2,3)$ to the plane equal to 2. I tried ...
6
votes
3answers
4k views

Summing along rows or columns of a matrix

I have a list of rows in database such as {{a,b,c}, {d,e,f},{g,h,i}} I want to be able to add each row across and each column down (like a spreadsheet). In other ...
0
votes
1answer
396 views

how to work with list as function parameter

I want to output an arrow based on input from user and I tried writing this small function to achieve this: ...
4
votes
2answers
901 views

Selecting multiple columns from a matrix?

Sample data: ...
12
votes
1answer
384 views

How can I collect data for visualization of quick sort?

I know how to implement quick sort in Mathematica. But I don't know how to get the temp data for visualization, because I used recursion. I want the effect similar to this: ...
1
vote
1answer
162 views

ListPlot does not recognize my list

I have created a list in Mathematica and for some reason it does not want to Plot my list in pairs {x1,y1}, but instead does {y1,y2} even though I partitioned the list to make it in the correct ...
3
votes
4answers
317 views

How to change a value within a list of lists?

I essentially have two questions, both are related. 1) How do I change a value within a list of lists (I provided a example problem)? 2) Why does my code not work? I have a list which was created ...
28
votes
2answers
866 views

DeleteDuplicates not deleting duplicates

It is not surprising that DeleteDuplicates[{5,5.}] returns {5,5.} because DeleteDuplicates ...
0
votes
2answers
717 views

Assign the output of a loop [duplicate]

Possible Duplicate: Creating a table/Matrix during a For loop Yet another simple question. ...
6
votes
6answers
447 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, ...
3
votes
2answers
513 views

How can I transform a list of binary digits into integers?

I want to transform a list of binary digits into integers. With the Table function, I produce four lists of binary digits of length 32. Then I tried to turn these ...
1
vote
1answer
135 views

How can I make my code simpler?

I want to find similar letters ...