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

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3
votes
4answers
174 views

How to combine the elements of two lists using a user-specified function

I have two lists of integers. From these lists I want to produce a list where each element is a fraction derived from a corresponding pair of elements in the original lists, the smaller integer of the ...
1
vote
2answers
217 views

Manipulating elements of a matrix, to loop or not ?

I have a grid of values generated from a MATLAB evaluation. Most of these elements are 0, some 0.5 and the remainder 1. I'd like to write a mathematica script which reads in the CSV and then, in every ...
0
votes
2answers
73 views

How to change list to a list of points

I have a list of angles {a1, a2, .... , an} and I would like to have a list of points ...
1
vote
4answers
120 views

Group data in table by 2nd column while consolidating values in 3rd column

I currently have a list in the format: {Group, State, num} {{a, CA, .5}, {a, AK, .2}, {a, MX, .1}, {b, CA, .8}, {b, AK, .8}, {b, MX, .1}, {b, HI, .7}} I ...
2
votes
1answer
70 views

Listing all values in an array

I am trying to populate an array variable using a do loop as follows Do[rayseg[1, i] = i, {i, 1, 5, 1}] This does what I want it to do, however I want to be able ...
3
votes
3answers
183 views

Change matrix elements at specific locations?

Let's say I have an array a={{1,2,3}, {4,5,6}, {7,8,9}} I want to have all elements along the diagonal multiplied by 2. ...
0
votes
3answers
83 views

Delete nested lists with Missing[“NotAvailable”] [duplicate]

I have a list of stock symbols and related information containing some entries Missing["NotAvailable"]. I would like to delete all nested lists which contain a ...
0
votes
1answer
116 views

Select nested lists based on string pattern

I would like to select nested lists out of a master list based on certain string pattern as in the following example: ...
1
vote
2answers
192 views

How do I disorder a list in Mathematica?

Given a list like this (the original list is much longer), how I can get a completely unordered list and save it in plain text? I change the file names (names at random), using a length of 5 digits, ...
0
votes
1answer
66 views

Selecting elements from a list [duplicate]

I have the following array of numbers: a = {{0, 2, 5}, {3, 5, 1}, {4, 0, 5}, {8, 3, 4}, {0, 8, 6}}; then I make a list of the first row with ...
0
votes
0answers
67 views

Improve performance of processing transactions in a large file

I want to work with a table which has 296,705 transactionslines and 172,147 transactions. ...
2
votes
1answer
100 views

Removing characters from non-strings

I have a large list of lists that contains mixed data, some real, some strings. The lists are of various lengths and depths. Some of the real data values have an asterisk appended to them, e.g.: ...
0
votes
2answers
92 views

Select over many lists with changing selection criteria

I have many individual timeseries I am trying to align and compute the mean and other statistics for. The problem I am having is that I am only interested in aligning a particular part of each ...
1
vote
1answer
63 views

Export nested list with complex structure

I have a list that looks like this l = {elem1, elem2, ...} Where elem_={t, {d1,d2,d3} } How can I export it? I tried ...
1
vote
1answer
55 views

Let's do this list-rearrangement prettier [duplicate]

Suppose that i have a list in this format= $list=\{ \{a,obj1 \} ,\{c,obj2 \}, \{a,obj3 \}, \{b,obj4 \} \dots\}$ I want to construct a new list in this way: $ newlist= \{ \{ \{a,obj1\} , \{a,obj3\} ...
6
votes
6answers
522 views

Determine if all the zeros in a list occur at the end

I have a collection of (short) lists of nonnegative integers. For each, I would like a predicate that decides if all of the zeros in the list appear at the end. For example, ...
8
votes
3answers
432 views

How to build a matrix from a set of vectors and other matrices using ArrayFlatten

I want to build a 6 by 3 matrix, from the following: one vector is 3 by 1, then a matrix, which is 3 by 2. These will go to the top 3 rows. Now the bottom 3 rows, I'll have 3 vectors each is 3 by 1. ...
2
votes
3answers
140 views

How to extract both first and last rows of each group from unbalanced panel data

This is a follow up question form my last question click here. I have unbalanced panel data such as : ...
7
votes
2answers
301 views

Generate cyclic list from a list

Given a list (for example, {3, 5}) I would like to make a function genCyclic[n_, list_] which generates a cyclic patterns of ...
1
vote
0answers
100 views

Find algorithm or generator formula with automated procedure and pattern recognition

I am trying to find a generator formula for the discriminant of a polynomial and believe it would be an interesting problem for the Mathematica community to know how to automate evaluation of certain ...
5
votes
4answers
235 views

How can I get a list of the positions of the running minima in a list?

I want the positions of the (sequential) running minima in a list, that is, the positions of entries that have the minimum value of all the elements in that list, up to and including that entry. For ...
3
votes
3answers
344 views

List manipulation: Dropping first or last row or column of a matrix

How do I drop the first/last row or first/last column from a matrix? The general case is answered here but I am new to Mathematica and it the arbitrary case is unnecessarily complex. Suppose I am ...
0
votes
1answer
73 views

Elements inside arrays seem to be strings rather than signed numbers

When I have code like b = Array[Subscript[be, #] &, {3, 1}] b = b /. {Subscript[be, k_] :> Subscript[-be, k] /; k > 1} I am noticing that Mathematica ...
4
votes
3answers
224 views

Replace elements in matrix to make it symmetric using automated procedure

I am generating a matrix using (mat2 = Array[Subscript[a, ##] &, {4, 4}]) // MatrixForm but would like to force Mathematica to make it symmetric. Thereby I ...
0
votes
2answers
76 views

Constructing a table from a constraint on another table

I have a 1000X6 table, where in each row the first three columns are dependent on the second three. I then make smaller tables of 1000X2 from these first three columns and basically ...
1
vote
3answers
210 views

Defining functions when there are a lot of parameters

Suppose I have two lists of parameters: $\delta=\{\delta1, \delta2, …\}$ and $\gamma = \{\gamma1, \gamma2, …\}$. The question is: how can one use $\delta$ and $\gamma$ (the parameter vectors) within ...
1
vote
2answers
66 views

Inconsistency in arithmetic on list elements [closed]

As expected, {a,b,c} - {a,a,a} (* {0, -a+b, -a+c} *) Or the same result can be obtained with less typing, thanks to implicit duplication of the subtrahend: ...
2
votes
2answers
97 views

Inverse of Times->Sequence

Suppose there is a list list={abc} then the replacement Times->Sequence gives ...
7
votes
3answers
401 views

Functional equivalent of a For loop referring to consecutive elements in a list

I have implemented this function which smooths the values in a list by, if it encounters a zero, replacing this entry by the average of its two neighbours (apart from the first and last values of the ...
1
vote
1answer
98 views

Replacing Logic operator List and generate combination of variables

so I'm trying to do the following starting from a list of inequalities: ...
15
votes
1answer
290 views

The efficiency compare between Flatten[#, 1] & and Join @@ # &

Err..Often I met the situation to join lists at the first level and I used to just Flatten[#, 1] &@ them. However, I found(when glance over the mathematica.stackexchange.com) someone else prefer ...
0
votes
0answers
23 views

Manipulating nested matrices columnwise [duplicate]

I have a project that requires analyzing large volumes of excel sheets at the same time. I have been having trouble figuring out how to index the imported files and manipulating them. The way I am ...
6
votes
4answers
179 views

Duplicate mapped elements in Riffle

What is the best way to do this? in: {a, b, c} {d, {e, f}, g} out: {{a, d}, {b, e}, {b, f}, {c, g}} ...
12
votes
2answers
319 views

What does IndexBy do and how exactly does it work?

I just saw the function IndexBy in the autocomplete suggestions and I was curious to know exactly how it works. Unfortunately, there's no trace of it in the ...
10
votes
5answers
438 views

How to randomly select subsets

I have a list of around 300 elements. I want to sample subsets of length 25 such that my samples are all distinct. My first inclination was to use something like ...
4
votes
1answer
127 views

Output function control and manipulation for efficient computation [closed]

I have taken note of a similar post related to modifying function parameters. I tried to adapt Kuba's solution to this post but I can't get it to work. I will illustrate my problem using a similar ...
2
votes
3answers
579 views

Plot a table of lists

I want to make a point plot of a table with lists in it. Assume I have data like this: data={{1,2,3,4},{5,6},{1,5},{2,4}}; and now I want to make a point plot ...
0
votes
2answers
57 views

Table results within loops

I have the following code. ...
0
votes
1answer
206 views

Iterating over a 2D list [closed]

I want to collect the result of a function in a data structure. In java the loop looks like the following code: ...
0
votes
1answer
62 views

Compute the evolution of several quanties from a data file

This question is somehow a part II of this: Part I. Here comes a small data sample as a minimal working example: ...
1
vote
3answers
261 views

How to select elements from a list by condition?

Considering I have a list: F = {f1, f2, f3, f4} I want to perform exponent on the list F = Power[#, 2]& /@ F Now I ...
2
votes
4answers
204 views

Pure function, one slot refers to List-position

I used all my google-fu trying to find how to make this work; read the docs as well. What have I missed? I feel sure this can't be a new question, but I can't find anything Here is is: ...
7
votes
2answers
1k views

Dramatic speed difference of code on Matlab and Mathematica

Background: I was trying to convert a Matlab code (fluid simulation, SPH method) into a Mathematica one, but the speed difference is huge. Matlab code: ...
1
vote
0answers
66 views

List manipulations with ; and ;; [closed]

I have the following list: L = {{a1,a2,a3,a4},{b1,b2,b3,b4},{c1,c2,c3,c4}} By using just the ; or ...
0
votes
1answer
469 views

Making table and plotting results of NDSolve problem

I am trying to solve two equation to find /[Phi][x] and plot h vs. /[Phi][x] for different values of L.I tried by writing as: ...
0
votes
1answer
65 views

Code optimization, Pad missing keys and Total part of values [closed]

Code optimization, Pad missing keys and Total part of values ...
1
vote
2answers
72 views

Encoding variables

I'm trying to fit a Logistic Model using LogitModelFit in Mathematica. The data I'm using contain qualitative variables that I have to encode. I've searched in ...
3
votes
1answer
208 views

Functional programming approach to avoid traditional loops

I'm currently learning from the wonderful post: Where can I find examples of good Mathematica programming practice? And i'm correcting my habits using Nest/Map/Thread instead of loops. The problem ...
2
votes
1answer
250 views

Appending elements to a list in parallel table

Is there any way to store values in a list that is being computed in parallel? For example, if ParallelTable is computing some ...
0
votes
2answers
134 views

Contract two lists

Suppose I have two lists of the equal length in the form powers= {{rho th},{mu},{beta},{nu},{r},{}} ...