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

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17
votes
12answers
2k views

Pick elements of largest absolute value

For example, given list = {{1, -3, -5}, {2, 1, 6}, {0, 2, 4}, {-9, 2, 6}} should return: {-5, 6, 4, -9} Updated I found ...
4
votes
0answers
167 views

Replacing and combining elements in a list [duplicate]

I am trying to increase the level of nesting in the following list while adding a 'tag' to each leaf: ...
1
vote
0answers
35 views

How to divide all rows of a matrix by their row sums [duplicate]

I've got a general matrix K that I would like to divide it's row's by the row sums of the matrix. I could get this going by doing ...
5
votes
2answers
506 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? ...
0
votes
2answers
134 views

List manipulation - End loop

Given are two matrices (a & b). I want to end the For-loop if all values in the matrix (a minus b) are smaller than 7, in contrast to any value in the matrix (a minus b) is smaller than 7. Can ...
2
votes
1answer
451 views

Extracting a range of data from a table

I have text file with data in 2 columns. I have imported it using the following line c = Import["ab", "Table"]; This text file has a large amount of data, and I ...
1
vote
1answer
206 views

Map a function conditional on elements at multiple relative positions in a list

I figure this question has many solutions, and if an answer already exists it would be nice just to be referred to it. I need a function that 'maps' over my list and produces a list of equal length ...
4
votes
2answers
256 views

Can someone explain this code for joining two lists by the first element of each sublist?

Background (which may be skipped, unless context is needed) I've recently begun learning Mathematica (and only up to chapter 3 of Wellin), but wanted to write some code to get a better feel for ...
1
vote
1answer
81 views

Create a new list under conditions from an existing one

I have an external file (data.out) which I read it with Mathematica using data = ReadList["data.out", Number, RecordLists -> True]; This file contains three ...
8
votes
3answers
202 views

Select and Blank

I try to filter sublists of a list which match a pattern. test = {{"String1", "a"}, {"String2", "b"}, {"String3", "a"}, {"String4", "a"}}; The result should ...
4
votes
4answers
166 views

Robust function for manipulation of nested lists

I have a nested list of the form: ...
2
votes
1answer
217 views

How to compute a discrete histogram of a list [duplicate]

I'm trying to compute the discrete histogram of a set of values. By histogram I mean the absolute frequency a value appears on the dataset, by discrete I mean the values are from a discrete set, e.g. ...
0
votes
1answer
126 views

Reuse a dynamic list [duplicate]

Consider this Dynamic list ...
1
vote
3answers
265 views

Creating overlapped block matrices

I'm doing an FEM assignment using Mathematica. (EK1 = {{a11, a12}, {a21, a22}}) // MatrixForm (EK2 = {{b22, b23}, {b32, b33}}) // MatrixForm I don't know how ...
7
votes
3answers
2k views

Simulate MATLAB's meshgrid function

Here is MATLAB's meshgrid. I came up with these implementations in Mathematica: ...
1
vote
2answers
285 views

How do I create matrices with arbitrary list restrictions?

I want to randomly generate a square matrix of dimension n with entries in the list StartingEntries, and also satisfying that for any such matrix M, the matrix Inverse[IdentityMatrix[n] - M] has ...
8
votes
3answers
192 views

Preserve information in flattening a nested list

I have a series of lists in the form below: list={ {1,1} , {2,2}, {3,{3,1},{3,2},{31,{31,1},{32,2}}} } Its a nested list which the dimension is changing case to ...
4
votes
4answers
262 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 ...
0
votes
2answers
155 views

Compute percentages in a list

I have a data file which contains thousands of lines and each line has eight elements. Here is a small sample of the data file ...
1
vote
1answer
196 views

ListPlot under conditions Part II

I have a data file containing several columns and thousands lines of data. Below I present a small portion of it, in order to express my issue: ...
4
votes
4answers
269 views

Generate Non-Singular Matrix of $n*n$ dimension

I want to create a function that will make an $n*n$ matrix which is non-singular that will always retrieve the same matrix (meaning that the matrix will not be random each time). I tried using the ...
12
votes
5answers
530 views

Filtering elements from a list that appear only once

I want to be able to select elements from a list that only appear once. I originally had this: Select[Table[Count[list, i], {i, list}], # == 1] But the issue is ...
2
votes
1answer
140 views

Match a sequence of integers

I would to match a pattern p1 = 0,0,1,0,0 to the elements in listA. The elements are a boolean sequence that may look like this ...
-1
votes
2answers
100 views

Manipulate store values

Is there a way to store the numerical values from a manipulate function in the form of a table? For example, if the function is f[x_] := x^2 - 2x Can one store ...
1
vote
2answers
143 views

Creating a Table of Items for GIF creation

I want to create a table as shown below so that the steps from the first item to the second item, and the second item to the third item, etc. can be animated. I am not at liberty to post tested ...
2
votes
1answer
109 views

How can I make check boxes that put elements into a list?

Right now I have a blank list that I am putting in Manipulate[]. I want to be able to choose whether 1,2, or 3 are in this list by setting z1,z2, z3 as True or False: ...
21
votes
4answers
721 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 ...
3
votes
8answers
253 views

How Do I Perform Simple Operations On The Elements of a Table?

I have been using the function HistogramList to generate frequency tables off a data set. The code looks like this: ...
9
votes
5answers
393 views

Count consecutive occurrences in a list above a certain value

I am trying to tally and sort the number of consecutive occurrences in a list above a certain value. For instance: ...
1
vote
1answer
173 views

Create continuous function from list

I have a list of data (measured per day) that I want to use as imput for another equation (say f). The problem is that the input I need for f needs to be a continuous function of time. Is it possible ...
20
votes
7answers
827 views

Make a huge vector in a wise way

I need to construct a vector similar to: v[x_]:={0, 0, x, 0, 0, 2*x, 0, 0, 3*x, ....., 0, 0, n*x}; where n=10^9. How can I ...
18
votes
1answer
384 views

Underlying Algorithms for List Manipulation Functions

Does anyone know, or know of a link for the underlying algorithms used for list manipulation functions? Specifically: Union with and without the ...
8
votes
3answers
779 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 ...
8
votes
6answers
218 views

Custom Matrix product

I have a list: list1 = {{{a1, a2, a3}, {b1, b2, b3}}, {{c1, c2, c3}, {d1, d2, d3}}}; I want an operation that gives me: Is there a built-in way of doing ...
5
votes
3answers
290 views

Drawing CountryData groups

I'm sure I'm overlooking something obvious, but I can't draw groups of countries. Here are two countries and two country groups: ...
5
votes
8answers
446 views

Extracting matrix rows when one of its elements is part of a list (without a loop)

I have a matrix whose rows I want to extract based on whether the elements of one of its columns is a member of another vector (calling it the "comparison vector"). I would like to get better at ...
0
votes
0answers
64 views

Defining functions in a loop [duplicate]

I have a symbolic solution to a linear system with respect to some variables a[i,j] which depend on a parameter t. sol=Solve[...,Table[a[i,j],{i,0,n},{j,0,n}]] I ...
3
votes
2answers
104 views

Linear interpolation of a list between periodic anchorpoints

I have a list of the form: list = {1,1,1,2,2,2,3,3,3,4,4,4,7,7,7,19,19,19}; Where we can see that there are an ordered set of integer values that repeat ...
2
votes
1answer
113 views

How to make a list/matrix out of an expression?

I would like to make a matrix out out of the following expression: $$ (\Omega^2 (2 d\theta^2 + d\phi^2 - d\phi^2 \cos(2 \theta) \coth(\chi)^2) + (2 d\Omega^2 + (2 d\theta^2 + d\phi^2 - 2 ...
1
vote
2answers
359 views

select subsets of elements of a list under a certain condition

I am new in Mathematica and am stuck on a simple problem. Please advise: I have the following list: list = { {"1", 1000}, {"2", 800}, {"3", 800} }; I want to ...
3
votes
0answers
150 views

List manipulation, replace a value [duplicate]

I have the following list: ...
4
votes
4answers
413 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
1answer
141 views

Value for x such that |(x-y)| is minimum

I have a list Y={y1,y2,y3,...,yn} And I would need to find x such that Abs[x-Y[[i]]] for all $y_i$ in $Y$ is minimum. ...
4
votes
1answer
383 views

Counting the number of operations performed during a calculation

I need to know how can I count the number of operations performed during a calculation of a CompoundExpression. In some of these expressions there are ...
2
votes
4answers
227 views

Removing coefficients and repeated elements

I got to a problem where as I just can't find the proper Mathematica command. I'm given a list, for example: $\{1,x1,-x1,x2,x5,x3,-x2,-x4\}$ I need this to become $\{1,x1,x2,x3,x4,x5\}$ The ...
0
votes
1answer
242 views

How can I build a GraphicsGrid of fixed size that rearranges the empty plots?

OK, let's make one final attempt; they say the third time is the lucky one! Following @rm-rf 's suggestions, I will try to be as clear as I can. My Mathematica code reads and plots simultaneously ...
3
votes
7answers
649 views

Finding the midpoints of an ordered list of numbers

Suppose that I have an ordered list of numbers. The numbers in the list may be evenly spaced, but they may not be. Here are two examples, list1 and ...
2
votes
2answers
378 views

How can I build a GraphicsGrid of arbitrary size?

This is actually a very simple scenario, in order to make simpler this question Part I. Consider the following piece of Mathematica code ...
3
votes
4answers
230 views

Test whether date is in a certain period

I have one table which contains time periods ("start" and "end") and a "type" for every ...
1
vote
2answers
99 views

Making two lists which share part of its name, while its name is also an element of the list

I am stalled with the following problem: I want two lists, for example: name={1,2,3} and namec={{1,2,3},{x,y,z},name} The ...