Tagged Questions

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

124 views

Recursive list contruction

I am attempting to implement the exercises from The Little Schemer in Mathematica, and running to a bit of a challenge with rember (remove member). Given a list and a value, the function just returns ...
196 views

Removing elements from a nested list based on their global count

I have a very large table containing sublists, such as for instance: {{1, 2, 3}, {4, 5, 6, 7}, {1}, {1, 8}, {9, 10}, {11, 6, 12, 13, 14, 15, 16}} I want to ...
252 views

Fastest way to sum the upper triangle

I feel like this is an recurring question: if there's a symmetric matrix whose diagonal is not all 0, how could I get the sum of the part of it that's above the diagonal as fast as possible? Small ...
610 views

When to use @@@ vs. /@ [duplicate]

So much thanks to Szabolcs in improving sequence.. for complete explanation. I am so glad to read all explanation which fundamentally remove the problem. But in number 4 of its explanation pointed to <...
432 views

delete zero rows in a matrix

If there is a matrix with some of its rows equal to zero: (its zero rows are randomly distributed and does not have an ordered arrangement): same as: ...
51 views

Adding up a list of subscripted elements [closed]

I have a list of entries with subscripts. I want to add just the entries. How can I do that in the presence of subscripts? For example: list = {1a, 2b, 3c} And ...
100 views

How to compare and remove x-coordinates (and the associated y-coordinates) that are less than previous x-coordinates?

I am using Mathematica version 9.0 and am trying to compare and remove x-coordinates, and the associated y-coordinate, that are less than previous x-coordinates. Below is an example using sample data. ...
55 views

Deleting duplicates of plus or minus symbolic quantities from a list [closed]

Let's say I have a list l = {a + bc - d, -a - bc + d, a + b};. Now I want to apply DeleteDuplicates[l, crit] to this list, such ...
198 views

I have ...
54 views

Transform a vector DE into a set of scalar DEs [closed]

I have the vector equality: {{a,b},{c,d}}.D[{x1[t],x2[t]},t]=={{e,f},{g,h}}.{u1[t],u2[t]} I want to solve this using DSolve. ...
53 views

Saving Dot-ed eigenvectors in a special comparison

We have produced a 4*4 matrix in any iteration containing nx from 0 to 2 by steps of 0.5. and in any iteration we have saved sorted orthogonalized-eigenvectors based on their eigenvalues with this ...
253 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 ...
332 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: ...
92 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 this....
69 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: ...
161 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 ...
76 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 : ...
264 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 ...
56 views

Position not working? [closed]

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: ...
94 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 ...
252 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 ...
61 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 ...
70 views

Count participation of variable list

I have the directed edges of a graph given by a list of variable (vertex) pairs. ...
64 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 ...
250 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 ...
121 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 ...
82 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 ...
256 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 ...
159 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 ...
67 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 ...
32 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 ...
114 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 <...
66 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, ...
182 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_ ...
155 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 ...
154 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: <...
78 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 ...
204 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 ...
245 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? ...
106 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 ...
179 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 ...
539 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 ...
60 views

Dynamic insertion of variables

I have a list of eigenvectors of a given matrix. I need to programmatically modify this list by multiplying each vector by a variable #i, e.g. ...
65 views

Changing the precision of data in a list of matrices

I have a list of matrices ...
443 views

List manipulation challenge

It's necessary to get from list = {{a1, b1, c1}, {a2, b2, c2}, {a3, b3, c3},{a4, b4, c4}, {a5, b5, c5}}; I'd like to do this with ...
87 views

Is there a way to create a table where the number of dimensions is parameterized?

I'm imagining the likes of this: ...
72 views

Module using for creating a table [closed]

I want to have a 4 tables with using of module. Unfortunately I don't know why doesn't it work ...
91 views

List of list to list of rules

I have a list of this type p = {{y, 1, 3}, {x, 2, 0}, {z, 3, 1/(k + 1)}} I can use a Do loop that is ...