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

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3
votes
3answers
461 views

Efficiently compute double sum

Is there a "Mathematica Way", like Map or Apply to compute the following double sum? $\sum_{i=1}^{N_1}\sum_{j=1}^{N_2} m_i n_j \, f(\tau_{i} \gamma_{j})$ I have already stored the lists ...
3
votes
4answers
195 views

Trouble with Position[] [duplicate]

I am in trouble with Position, Although my example works as expected it throws a warning. Position[{{a,b},{a,c},{a,b}}, _?(#[[2]]==b&), {1}] During ...
0
votes
2answers
35 views

“Part specification is longer than depth” warning in Position function [duplicate]

I'm working on a project which analyzes financial data. I download the price and dividend information for the SPY ETF which tracks the S&P 500: ...
2
votes
2answers
49 views

Displaying a list of percentage values according to their classification

I have a list of percentages as follows: percent = {21.15, 42.3, 57.68, 73.06, 84.6, 90.37, 96.14, 99.99, 99.99, 99.99, 99.99} I want to classify these ...
2
votes
1answer
106 views

Dirichlet convolution of two lists [closed]

The Dirichlet convolution of two arithmetic functions f,g is defined by $f\ast g(n) = \sum\limits_{d|n} f(d)\ast g(n/d)$ How can I get the Dirichlet convolution of two lists? For example: Input: ...
2
votes
2answers
140 views

Efficient List of Lists

I'm running some analysis that requires the creation, row by row, of a large list of lists. The big list is called "Nodes" and it will ultimately contain hundreds of thousands of rows. The first few ...
1
vote
2answers
64 views

How to find the same number in sublists of list

Intersection[Table[Table[Sqrt[p1]/r1,{r1,0.1,0.7,0.1}],{p1,0.5,5,0.5}]] I am trying to find same numbers in the sublists. But Intersection is not working for ...
1
vote
1answer
45 views

calculate relationship between cause and effect (rows/columns/delta etc.) on tableform

I tried to enter this Excel (on the right of the picture) information to program. following these codes has been used: ...
6
votes
2answers
57 views

How to count the number of values in a discrete function?

I have a discrete function of an integer variable $n$ defined like this : ...
4
votes
4answers
231 views

Replace matrix rows conditionally while avoiding For loop

I have the following variables: myMatrix={{0,0,0},{0,0,0},{0,0,0},{0,0,0},{0,0,0},{0,0,0}} myIndices={1,3} I need to replace the rows ...
-1
votes
1answer
43 views

Position not working? [on hold]

I have the list: myList={0,0,0,a,b,c,0,0,d} I need to find the positions of all elements that are non-zero. I do like this: ...
12
votes
1answer
173 views

ListConvolve Memory Hemorrhage

Bug introduced in 10.0.0 and fixed in 10.2.0. I wrote a routine that convolves an impulse response array with a test array and checks for the RMS difference between that convolution and a data ...
0
votes
0answers
48 views

How to replace element by element in a list? [on hold]

I have the list: myList={{a,b,c},{d,e,f},{g,h,i}} I need to transpose every element individually, so I do: ...
8
votes
4answers
325 views

Unexpected behavior from GatherBy in version 7

Bug introduced in 7.0 or earlier and fixed in 8.0.4 or earlier I have come across what appears to be a bug in GatherBy. It appears similar to the problem of ...
6
votes
1answer
65 views

Problem Using Evaluated Replace with Associations

If I define some function like: toISOdate[data_List]:=DateString[data,{"Year","-","Month","-","Day"}] and try to applicate it in an ...
12
votes
9answers
486 views

Generating a matrix using sublists A and B n times

I want to write a function that generates a square matrix from sublists. My sublists are a = Range[0, x, 0.5]; b = Range[0.25, x + 0.25, 0.5]; Suppose x=2, then I ...
1
vote
1answer
120 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 ...
5
votes
3answers
220 views

How to imitate list comprehensions for constant arrays?

In Python, ['a'] * 10 generates ['a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a'] and ...
4
votes
2answers
46 views

Inputting values into the variables without having to input the matrix all over again

I'm practicing using LU decomposition on Mathematica. I am able to find the L & U matrices, specifically the variables. However, i find it tedious having to input the newly found values and form ...
3
votes
2answers
72 views

Find sub-sets of vanishing additions or subtractions from a list?

Let's say I have a list L containing n numerical numbers. Now I want to find all sub-sets of ...
0
votes
1answer
57 views

Count participation of variable list

I have the directed edges of a graph given by a list of variable (vertex) pairs. ...
2
votes
1answer
45 views

How to extract part of association?

Considering an association: asc = <|"a"->1, "b"->2, "c"-><|"e"->3, "c"->4|>, "d"->5, "e"->6, "f"-><|"g"->7|>|> How ...
5
votes
3answers
152 views

List all “duplicate” elements in Tally

Tally[list,test] can use a custom function test to judge if elements are equal. But the output will only give the first element ...
2
votes
1answer
107 views

How can I write a loop to get many values from a solution?

I am looking at the value of x[t] at day t = 200 over several years. I tried to do it using a For-loop but it didn't work. This ...
0
votes
0answers
35 views

Binomial decomposition of a list? [closed]

Given a list L with n elements, I would like to generate all possible unordered subsets of ...
3
votes
3answers
132 views

Find position avoiding For loop

I have a list: {a,b,c,d,e,f} And a function sizeFunc[element_] which returns the size ...
2
votes
2answers
50 views

Import a column of data, make a matrix from it and export it WITHOUT curly braces

I'm new here and with Mathematica, too. I want Mathematica to import data from a txt file (it has one column of data). These entries are z-values. From this I want to make a matrix - 508 entries make ...
2
votes
1answer
43 views

Dropping rational coefficients

I have a list of expressions (they all are exact numeric quantities, not containing any variables), some of them have integer or rationals coefficients, or complex coefficients with rational or ...
10
votes
2answers
3k views

How to get Matlab data imported with the same dimensions?

I have some Matlab image data with the following dimensions (output is from Matlab): >> size(im) ans = 86 86 3 45 The data imports just fine ...
1
vote
0answers
28 views

Accessing the elements of a list of values [closed]

I have a list of polynomials (all with the variable x) called lyle and a function that accesses this list and evaluates it at ...
0
votes
2answers
253 views

Animate a sequence of bitmap-like data Mathematica 9.0.0

I am new to Mathematica, but already find it a very nice tool. Right now I am trying to create an animation of numeric data, where each frame corresponds to a distinct text file with a table-like ...
2
votes
2answers
95 views

Replace elements in some region in a list

I want to replace some elements in list. Assume that we have A={{1,2,3,4}, {5,6,7,8}, {9,10,11,12}, {13,14,15,16}} and we want to replace elements ...
0
votes
1answer
62 views

Match a variable name pattern [duplicate]

I have a list of variables: {RBI,RCD,ASD,FGH} I want to select only those whose name starts with R. Using the pattern Rx_ ...
1
vote
1answer
44 views

Sort and Save Matrices Eigenvectors to a Larger Matrix

We are going to sort and save all orthoginalized-eigenvectors of 4*4 random matrices (produced in any iteration) to a larger matrix such as storagematrix. Since, produced random matrices are 4*4, ...
2
votes
3answers
499 views

For loop in Length computation code

Here is a code I wrote that is supposed to give the length of list after some splitting and regrouping. But it is inefficient. Is there a way to rewrite in more professional and efficient way? I guess ...
2
votes
3answers
114 views

Join nested lists based on first and last elements within each list

I have a nested list like this: test1 = {{1, 3}, {1, 4}, {1, 7}, {2, 1}, {3, 5}, {4, 1}, {5, 2}, {6, 1}, {7, 6}} I want to join the lists together depending on ...
12
votes
5answers
588 views

Is there a way to riffle more than two lists?

I thought Riffle would generalize such that Riffle[{a,b,c},{1,2,3},{x,y,z}] would return ...
9
votes
2answers
250 views

Is there a built-in equivalent to Python's enumerate?

Python's built-in function enumerate takes an iterable over $(a_0, a_1, \dots )$ as argument and returns an iterable over the sequence of pairs $((0, a_0), (1, ...
0
votes
2answers
49 views

Identify a scalar, a list

I have a symbolic scalar m2 and a symbolic list (representing a 3x3 matrix) A. I want a function which does something like: ...
7
votes
4answers
228 views

Improving a selection routine

How can this code for extracting the smallest (absolute) real value be improved? and would it be simpler using associations? ...
3
votes
3answers
149 views

Move element inside a list

I need to change the position of a single element in a list. Example: I start with: {a,b,c,d,e,f} I want to move the a before ...
0
votes
1answer
60 views

Do TakeWhile and LengthWhile work with Greater? [closed]

TakeWhile[{1, 2, 3, 4, 5}, # > 3 &] gives me {}. Similarly ...
1
vote
2answers
61 views

Convert a list of lists of rules to a list of values [closed]

I have a list of the following form: thisVeryExcitingList={{x->1},{x->2},{x->3}} I would like to convert it to the form ...
6
votes
1answer
181 views

Bug in LengthWhile?

Bug introduced in 8.0.0 and fixed in 8.0.1 Is this a bug or my MMA went insane or I'm missing something? LengthWhile[Reverse@IntegerDigits[1000], # == 0 &] ...
2
votes
3answers
180 views

Delete rows based on specific periods

I have data (.xlsx format): two columns - data in first column imported as DateObject (dates with specific time), data in second column are numbers (113388.28, 865165.98 etc.). I want to delete the ...
0
votes
3answers
76 views

Do not expand matrices in Mathematica calculation

Here is an example of a problem I'm having. Consider that I have defined: omega={{p[t]},{q[t]},{r[t]}} x={{a},{b},{c}} R={{1,2,3},{4,5,6},{7,8,d}} What I would ...
-1
votes
2answers
66 views

Delete Element within a List based on the Order [closed]

I want to do the following, deleting the element of a list that do not match an increasing order as example: {1,2,3,4,6,5,7,8}->{1,2,3,4,6,7,8} I've thought of using DeleteCases but I'm not able to ...
21
votes
2answers
856 views

How can the {x,y,z} points that fall on the outer boundary of a set of values be selected and smoothly surfaced?

For a given set of x,y,z values, that may, or may not form a uniform shape, how can the center of the data cloud be found, and the surface points be located and a solid smooth surface created from ...
29
votes
2answers
958 views

DeleteDuplicates not deleting duplicates

Bug introduced in 9.0 and fixed in 10.0.0 It is not surprising that DeleteDuplicates[{5,5.}] returns {5,5.} because ...