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

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5
votes
2answers
101 views

Comparison Operation for Nested Matrices

I have a nested matrix n as bellow ...
5
votes
3answers
241 views

How do I save/export a list so that it can later be easily imported as a list again?

I have a couple of big lists (each of them contains elements that are themselves lists of two elements, i.e. an element of each list that I have is of the form {x, y}) that I want to save/export. ...
0
votes
4answers
77 views

Drop row if sum of part of row is equal to zero

My problem is the following: Suppose I have a matrix A which looks the following: ...
26
votes
3answers
2k views

Data Table Manipulation in Mathematica

I am a statistician searching for an efficient way to select rows or columns from a table of data in Mathematica. Let me pose the question in 2 parts with a SQL-style table of data: ...
4
votes
6answers
404 views

Insert all elements from one matrix into another

I have two matrices $A$ and $B$ which are the same size. Each element of $A$ is a list of numbers. Each element of $B$ is just a number. How do I insert each element of $B$ into the corresponding list ...
0
votes
1answer
68 views

Matrix operations performed with column-vectors

We have 3 matrices: m1, m2 and b. We want to apply matrix operations (dot or sum) in a ...
0
votes
1answer
52 views

Assign values to variable names in lists

I hope somebody can help me in this (I guess) simple question: I have a list of variable names ls={w0,w1,w2} and another list of values ...
0
votes
2answers
78 views

How do I sum up p items in a sequence?

I have the following sequence list = {p1, p2, p3, p4 ....} I am summing up the p items as follows: p1 + p2 + 2*sqrt (p21*p2) = p12 p12 + p3 + 2*sqrt (p12*p3) = p123 p123 + p4 + 2*sqrt (p123*p4) = ...
4
votes
2answers
233 views

How can I create a class of matrices programmatically?

I am trying to figure out how to create a function that can create the matrix pattern below, where: f[1] returns {{1}} ...
5
votes
3answers
236 views

Nested list to graph

The following nested list can be regarded as a representation of a (tree) graph: ...
0
votes
2answers
87 views

Defining a function as a sum of several Gaussians

I have a function that is a summation of several Gaussians. Working with a 1D Gaussian here, there are 3 variables for each Gaussian: A, ...
2
votes
1answer
161 views

Deleting selected rows from data table [closed]

I'm an intermediate Mathematica user and the select function presented on Data Table Manipulation in Mathematica: Step 2 was very useful in helping me manipulate a 36Mb data file - 13 columns and 180k ...
1
vote
1answer
52 views

Elements of a List according position in axis

({{a, b}, {c, d}}) a, b, c and d are Lists of 300 length. Their first 4 elements must specify their position in the column (1 column, 2 column, etc) and the ...
2
votes
3answers
268 views

Introduction of straight Line into Manipulate function

I just want to implement a line within my chart that starts from time point 0 to time point T and whose y-coordinates can be manipulated, which in my case is represented by D. I tried to implement a ...
2
votes
2answers
81 views

Select words from different rows of column headings

I have a 2-dim array. The first 3 rows have column headings. The heading can be a single word, or 2 words (which take 2 rows) or 3 words (which take 3 rows). For each column I know which row has ...
10
votes
5answers
427 views

How would you efficiently implement BinListsBy?

Let's say I have a list like this: data = {{21, "Alice"}, {27, "Bob"}, {22, "Charles"}, {34, "Dora"}, {75, "Eliza"}} containing ages and names of persons. What I ...
1
vote
1answer
80 views

Nest Replace Function with different rules

I have a table of data that I want to filter. Any value of zero in the table means that value was not calculated, so it should get populated with the tag "NC". Next the table is filtered for all ...
2
votes
2answers
100 views

What is wrong with my use of Flatten? [closed]

Why does Flatten[f[g[a, f[b]], f[c, d]]] result in f[g[a, f[b]], c, d] I expected the answer to be ...
3
votes
2answers
96 views

Find Lists with intersecting sublists

I have a list of the following form: ...
1
vote
1answer
70 views

Is this the expected behaviour from Partition when padding is inserted at the start of the list?

The documentation for Partition shows an example of partitioning without padding, so that no elements are dropped, but the last sublist can be shorter. ...
1
vote
1answer
117 views

Check every list element for appearance

I'm used to MATLAB so this might be a stupid question but Mathematica is freaking me out. I have a big matrix with the following format: ...
0
votes
5answers
81 views

Merge two lists for List3DPlot [duplicate]

I have a two lists: list1 = {{x1, y1}, {x2, y2}, {x3, y3}, {x4, y4}, {x5, y5}} and list2 = {z1, z2, z3, z4, z5} and I want to ...
0
votes
0answers
32 views

Grabbing columns from a matrix [duplicate]

If I have a matrix - exampleMatrix = {{A1,B1,C1},{A2,B2,C2},{A3,B3,C3}}; And I want to create a matrix like - ...
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 ...
3
votes
3answers
214 views

How can I extract multiple spans from a list?

I know in Mathematica, I can do A = Range[100]; B = A[[50 ;; 60]] B will then contain the 50th through 60th elements of A. Now, what if I wanted B to take 10th ...
1
vote
2answers
94 views

Clearing arguments passed to a Module

Is there a possible way to clear the arguments passed to a module to release some memory. I believe that arguments passed to modules are passed by value rather than pass by reference. e.g. I have the ...
2
votes
3answers
181 views

Using Part rather than Extract

In my work I found that I needed the Extract function. However I was wondering if there was a way to use Part. Assume that ...
4
votes
2answers
137 views

Replacing one element of list

I have a list of sequences of x's and y's. I want to switch the last position to the "opposite" symbol - if ...
3
votes
8answers
356 views

How to add a column to a table that counts the number of times the lines appear?

I am at a complete loss at this. I have a table with 2 columns and n lines. Some of the lines are repeated. What I want to do is add a new column that counts the number of repetitions of each line. ...
0
votes
2answers
106 views

Extract X value from corresponding Y value from a List or Transpose [closed]

I have a list of X values and Y values separately, and also together with: data=Transpose[{X,Y}] This data is from a chromatogram, and I want to extract the ...
7
votes
4answers
408 views

Generating an Ulam spiral

An Ulam Spiral is quite an interesting construction, revealing unexpected features in the distribution of primes. Here is a related topic with one answer by Pinguin Dirk, who has provided one ...
0
votes
1answer
70 views

Select duplicate values from a list [duplicate]

How can I select the duplicate values in a list? Example: {1, 2, 1, 1, 1, 1}
3
votes
2answers
226 views

Dealing with a huge dataset

I have two ingredients here: a big dataset contained in a list, with ~ 20M values. a function that takes as each element of the list as input and yields True or False I want to save somewhere the ...
0
votes
3answers
151 views

Trouble understanding a piece of code found on Wolfram Blog

I am trying to go through this Wolfram Blog example: http://blog.wolfram.com/2009/02/12/flag-analysis-with-mathematica/ on country flag analysis. I am having a problem understanding the following ...
1
vote
2answers
68 views

Replacing a specific pattern of values at level 2 in a list

I've a list of lists, tl = {{True, False, m12}, {False, m22, m33}, {m32, False, True}} and each nested list has the same length, What is the proper way to ...
2
votes
3answers
132 views

Delete Missing data from coordinate sets

I have a list of pairs of coordinates, where some are missing. ...
2
votes
2answers
151 views

Permuting elements within a list

I have s = {2, 3, 5, 7, 1, 4, 6} (* always with diffente elements in {1,2....7}*) l = Length[s] n = 3 and n tells us that we ...
5
votes
3answers
226 views

Split list of states by run lengths and discontinuous changes in state

I was asked to look into writing some simulation code for a user, where the simulation output (x) would oscillate between three possible states: ...
2
votes
2answers
93 views

Importing Data and Devoting Their Names to Them

There are some files in a directory. I have used of SetDiroctory to access all of them. SetDirectory["C:\\Users\\SE7EN\\Desktop\\mathematica\\test"]; I can visit ...
1
vote
2answers
147 views

Generating list of coordinates in $\mathbb{Z}^n$ given by set of inequalities

I am trying to generate list of coordinates that forms a subset in the integer lattice $\mathbb{Z}^n$. This set is given by set of inequalities. Right now, I am using the following: ...
0
votes
1answer
43 views

Resolving Error: Mathematica evaluation order on Lists

I have a table that is 27 x 27, each entry corresponds to an element from the periodic table. I use the replacement rules in element list to allow me to convert a list of elements into a list of ...
0
votes
1answer
151 views

How to load data into a Manipulate expression

I have data showing truncated octahedron geometry changing with time. How can I read those data into a Manipulate expression? To be specific, I want to manipulate ...
3
votes
2answers
181 views

make a list based on two other lists

I have two lists: list1={4,6} list2={1,2} and I now want a function f that produces f[list1_,list2_]:={1,1,1,1,2,2,2,2,2,2} ...
8
votes
4answers
290 views

Complement of multisets

Given lists $a$ and $b$, which represent multisets, how can I compute the complement $a\setminus b$? I'd like to construct a function xunion that returns the ...
2
votes
1answer
47 views

Complement for a Matrix

In a matrix, there are some non-zero elements same as: aA= Also, there is a list such as: list = {a, b, c, d, e, f, g, ii, jj, kk}; I want to access to ...
1
vote
0answers
38 views
4
votes
3answers
378 views

Efficient matrix / array generation

What is the most efficient way of generating the following matrix? $\left( \begin{array}{ccccc} 1 & 0 & 1 & 0 & 1 & 0 & 1 & \dots\\ \frac{1}{2} & \frac{1}{2} & 0 ...
2
votes
2answers
93 views

select from a list based on digits

I wish to know how do I count the number of occurrences of numbers that end in digits d. e.g. Say I create a list of Divisors of 12! I now want to count those divisors that end in 12. Like 12 & ...
8
votes
2answers
355 views

Aligning two lists

I have two lists, L1 and L2, each with a key and some data. Let us say the key is a person's name, a string, and the data follows. (To respond to rasher's query:) Let us also assume the lists are ...
0
votes
2answers
93 views

How do I perform the riffle function backward? [duplicate]

I know riffle will combine the lists {1,2,3} and {a,b,c} to be {1,a,2,b,3,c}. Is there a way to work backward and split the list {a,b,c,d,e,f} to be {a,c,e} and {b,d,f}?