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

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0
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0answers
28 views

Problem with slot in If statement [duplicate]

I am struggling with slots, In this case I have a function int which gives either true or false. When it gives true, I want ...
0
votes
1answer
60 views

Extracting second value of each sublist [duplicate]

How can one get the second value of every array inside the outside array? I have the following data data = {{10, 20}, {30, 40}, {50, 60}}; I want to extract ...
0
votes
1answer
56 views

Optimise CPU-intensive list combining function

I have a list of numbers list1 from which I want to create another list (list2) consisting of only those numbers that are equal ...
1
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4answers
169 views

Gather lists according to another list

I have a first list of pairs like this one: ...
0
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0answers
70 views

Generating the set of all three-dimensional binary arrays distinct under rotation and reflection?

How can I automatically generate all possible three-dimensional binary arrays of size $(x_1 \times x_2 \times x_3$) where each array is distinct from all others with respect to rotation and reflection ...
3
votes
1answer
199 views

Extracting function calls from an expression

I have an expression like this: expr = F[0, 1] + 2 F[0, 0] - 17*F[2, 0] and I want to transform it to a list consisting of all function calls with its arguments: ...
0
votes
1answer
42 views

How do I pull from a data list for parameter values in a system of ODEs and then solve and plot?

I have a parameter set list and I would like to solve a system of ODEs multiple times using each parameter set in the list. Then I would like each set of solutions to be graphed on the same plot. ...
-1
votes
2answers
167 views

Plotting solutions of differential equations with different parameters [duplicate]

I want to plot x[t], when i manipulate w from 0.1 to 1.5. Here is what I've attempted, which does not work as expected. ...
0
votes
1answer
97 views

Plot graphs in different colors

I am generating a set of plots and exploring how changing a parameter affects the plot shape. I want each plot to be a different color, but the color rule i'm applying seems to only work for the last ...
1
vote
1answer
189 views

GatherBy and two conditions

I have a list of 4 dim points, given by ...
1
vote
1answer
396 views

How can you convert a matrix back into a list of lists?

It is very simple in Mathematica to convert a list of lists into a matrix: all you need to do is apply the //MatrixForm function to it and voila. Is it possible ...
2
votes
3answers
307 views

Re-arranging / selecting of a data table very slow in For loop [duplicate]

My task is quite simple; I have a table of data like M = {{1,2}, {1,3}, {3,4}, {5,1}, {6,9}, {6,8}, {6,1}}; so the table is sorted with respect to the first ...
0
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0answers
34 views

Check if a (possibly nested) list is real [duplicate]

I have a very large matrix of numbers. I want to check if all its entries are real. At the moment I am using realQ = And @@ Thread[Flatten[Im @ #] == 0] & Is ...
9
votes
5answers
444 views

Take both of the diagonals through an element in a matrix

I have a matrix like this: Reverse@Array[List, {8, 8}] // MatrixForm I need a function that given an element of this matrix will return all the elements ...
1
vote
1answer
167 views

Splitting dates into groups in half year steps

list = DayRange[{1999, 1, 1}, {2014, 2, 6}] I want to split this list into sublists one and a half year long, moving a half year forward every time. That would ...
0
votes
3answers
149 views

Implementing nested subtotals

Inserting a nested subtotal in a spreadsheet is a facility that Excel performs very well. But if a subset of this facility can be implemented in MMA for a table which needs it the hassle of its ...
1
vote
2answers
84 views

Apply a function to each element of a list and sum it

I have a list {-1.8, 1.44, 0.2736, -1.72514, 1.17612} where each element stands for a value of x. e.g. $x1 = -1.8$, $x2 = 1.44$ and so on. How can I find the ...
2
votes
1answer
229 views

Finding the optimal teams ranking based on the table of match results

My original question was this: So my task is to score all the possible rankings of the 14 SEC football teams and find the best one, using who won in head-to-head games as the sole criterion ...
1
vote
3answers
461 views

How to expand the size of the matrix automatically?

I have a matrix in 2x2 a ={{x, y}, {z, u}} I want to expand this matrix 3x3 b ={{x, y, y}, {z, u, x}, {z, x, u}} 4x4 ...
3
votes
1answer
119 views

How do I get the length of held list without evaluating the list?

I used Extract with Hold to retrieve a sublist containing expressions I didn't want evaluating, e.g. ...
1
vote
1answer
130 views

Extra brackets of Position command

Command Position always comes with two extra curly brackets {{}} when it's just one index for the location. I use [[1,1]] in front of my position commands. Is there ...
6
votes
2answers
266 views

choosing the fastest way of finding position

I have this list {1,7,8,10} for instance. and a second list which is always smaller or equal to the first one say {10,7}. How ...
1
vote
1answer
98 views

A list containing zero elements

I have a list containing zero and nonzero elements. How can I throw away zero elements and just keep non zero ones.
2
votes
1answer
924 views

Contracting with Levi-Civita (totally antisymmetric) tensor

I have an array $v_{ijk}$ which is effectively a rank-$3$ tensor with dimensions $3\times3\times3$, and I need to contract it with $e^{ijk}$, i.e. evaluate $v_{ijk} e^{ijk}$ (see Einstein ...
2
votes
1answer
100 views

Explore a nested list

This question is similar to Numbering nested list according with Depth (or Level) I have a list like ...
0
votes
1answer
70 views

How to use ImageMultiply[] over a list of strings?

I'm trying to do the following: ...
6
votes
4answers
269 views

Using an ellipse as a threshold for Nearest function

The Nearest function can receive as a threshold parameter a radius to look for elements inside that. From the documentation: ...
0
votes
0answers
36 views

Updating List with Do works but not with ParallelDo [duplicate]

I am trying to find 5 minimas for some function. I can obtain the results if I implement a simple Do function. I tried to speed it up by using ParallelDo and then my code returns spurious results. ...
2
votes
3answers
315 views

How to transpose unequal lists

As the titel says I want to transpose a matrix containing rows of unequal length, to be able to transport them to excel (in row form, there are too many datapoint to write them in a cell. In another ...
2
votes
2answers
563 views

Fast way to extract data from a list

I used data=Table[{i,f[i]},{i,1,n}] to produce a list, here n is greater than 2^20 = 1048576. The function f(N) runs in time ...
4
votes
1answer
137 views

Searching for closest entry in a table

I have a large table of triplets whose structure is: list=Table[{a,b, RandomReal[]}, {a,1,100}, {b,1,100}] I would like to search through the list by looking ...
1
vote
1answer
128 views

Need help scoring randomly generated SEC football rankings

So my task is to score all the possible rankings of the 14 SEC football teams and find the best one, using who won in head-to-head games as the sole criterion (so not factoring in strength of schedule ...
0
votes
1answer
151 views

Generate encoding from nested list

Taking reference of Huffman code algorithm, ...
3
votes
4answers
351 views

How to apply a function of several arguments to a list?

I have a list of triplets: list = {{1, 3, 5}, {4, 5, 1}, {4, 9, 2}} How can I apply a function f to the last element of each triplet when f the last and ...
4
votes
2answers
208 views

How to set up and minimize a large system of equations to resolve the individual components

I am trying to set up a system of 400*N equations to deconvolute spectral data for four different compounds. I monitored 400 different wavelengths in N solvents (3 solvents in this case). In order ...
3
votes
2answers
234 views

List manipulation after importing txt-file

I have some problems converting data which I imported from a txt-file into proper Mathematica expressions. After importing my data looks like ...
3
votes
1answer
105 views

Recursion when randomizing elements in a list

I want to randomize certain elements of a list; Since the code list = {a, b, c, d, e, f, g}; list[[{1, 3, 5}]] = RandomSample@list[[{1, 3, 5}]]; list works fine, ...
1
vote
0answers
248 views

Convolve two sets of (x,y) data sets

I have two sets of data in the form a={{.1,2},{.2,3},{.3,4},{.5,6}} b={{0,8},{.1,4},{.2,7},{.3,1},{.5,10},{.6,3}} Both data sets have even spacing, although ...
0
votes
0answers
93 views
8
votes
3answers
314 views

Deleting quasi-duplicates from large list efficiently

I have the need to remove "duplicates" from large (>10K members) lists, where a "duplicate" is either a verbatim duplication, or the element's second entry exists as a first entry for some "earlier" ...
2
votes
3answers
139 views

Plotting lists, exact color values

I read some descriptions of similar problems but I cannot make them work in my example, I don't know why. I have list of 3 dim values to plot: x, ...
2
votes
2answers
119 views

Merge two Matrices without Duplicates

I have two matrices, for example: data1 = {{"c1", "c2", "c3"}, {2, 5, 3}, {54, 2, 3}, {11, 2, 10}, {3, 5, 7}}; and ...
1
vote
0answers
100 views

New list generated from the sum of elements taken from two lists

I have been using mathematica for a while, but I have problem wrapping my head around list manipulation functions. I would appreciate any suggestions. Here is what I want to do. ListV is a list of ...
-1
votes
1answer
116 views

Plotting the results of a system of equations

I believe this is a question of more list manipulation than plotting, but I hope you could help me. I solve numerically a system of equations of 3 variables, take only real solutions where one of the ...
2
votes
3answers
156 views

Join matrix based on conditions

Given the following matrix: ...
3
votes
4answers
217 views

Finding the location of the last day of the month in a list of dates

My question differs from earlier questions about getting the eom dates from a list; I want to get the position of those dates so I can get the corresponding values from other lists. My problem seems ...
8
votes
5answers
328 views

Manipulating a sublist based on position

I have a huge list with huge sublists of the form list={{a,b,c,d},{e,f,g,h},{i,j,k,l}} I am looking for a way to manipulate these sublists based on the positions ...
1
vote
0answers
34 views

How do I define a tensor from another tensor with summations? [duplicate]

Let's say we have a rank 2 tensor $g_{ij}$. This is basically a list with a Depth of 2. Now I'd like to calculate another tensor ...
3
votes
5answers
406 views

Minimum in a nested list [duplicate]

I have a nested list of {x,y,z} and I want to find out the values of x and y where z is minimum. I can write a nested For loop and do it ...
5
votes
3answers
185 views

Non-descending Tuples

I want to get all the non-descending tuples of a list with given length, for example: f[{1,2,3,4},{3}] ...