Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.
3
votes
2answers
108 views
Creating a list from other lists and varying the number of elements that get added
Suppose I have
listA = {M, F}
and
ListB = {a,b,c}
I want to make a new
...
4
votes
1answer
60 views
How do I group a nested list further according to a rule, and average selected elements?
I have a nested list of numbers like { {36, -244}, {37, -225}, {38, -197}, {48, -200}, {49, -181}, {50, -133} } which needs to be further nested into "bins" according to a rule. I would describe the ...
7
votes
3answers
160 views
How to add lists with unequal length?
Given lists of unequal lengths, I want to add them together element-wise, treating missing elements as zero. For example, {1, 2, 3} + {a, b} + {x} should give ...
2
votes
1answer
116 views
How to store values indexed by integer partitions for fast access?
I have a huge list of values indexed by integer partitions. If I store them simply in a list, then, when I want to access the value corresponding to some particular integer partition, I have to find ...
0
votes
1answer
54 views
How to extract data from a list? [duplicate]
I have a long list of coordinates defined in some 8D space. I need to extract the first three coordinates only. How ?
For example :
...
1
vote
2answers
85 views
How do I divide the columns of a matrix by the sum of its elements?
I am trying to create a transition matrix for a network. In order to do this, I need to sum down the column (the out degree), and then divide the column by the out degree in order to normalize it.
...
5
votes
1answer
167 views
DeleteDuplicates[] does not work as expected on floating point values
Here is my simple example, and in this case function DeleteDuplicates does not work as expected.
I want to FindRoot of my ...
0
votes
2answers
71 views
ListPlot of lists with specified x coordinate
I want to do:
ListPlot[{{x1, y1}, {x2, y2}, ...}]
each y being not a number but a list of numbers.
I tried:
...
2
votes
2answers
89 views
Preparing data for making an ErrorListPlot
I often have the following notebook in Mathematica, which I use to make a dataset and associated errors:
...
0
votes
0answers
44 views
Creating list within function [closed]
I'm probably doing something wrong here and would appreciate some insight into what!
...
2
votes
3answers
123 views
How can I name “a[[i]]” the parts of Table “a”? Or how to make Table “a” grow inside FindMinimum?
Let's say I want to minimize a function that uses a Table named a with the Conjugate Gradient Method of ...
3
votes
2answers
158 views
Adding and subtracting from elements in a list
I'm trying to solve an aparently simple problem.
Given a list of length n, {a1,b1,c1,d1...} I want to perform two simple ...
8
votes
4answers
106 views
Mark selected sub-lists in the list they were selected from
I've got this simple problem with two lists. I select some items from a list, but I want to visualize the difference between the previous list and the list that I create with ...
1
vote
3answers
118 views
Convert coefficients of polynomials into a matrix
I have several sets of 5 polynomials of the form:
...
12
votes
5answers
198 views
Faster way to convert triangle list to edge list with no duplicates
I have a list of triangles returned by a Delaunay triangulator, in the following format:
...
3
votes
2answers
138 views
Colors associated to parts of a 3D distribution of points
Suppose we have a long list of random points (cartesian coordinates) in 3D space.
coords := ...;
Until now, I was associating colors in a radial way, from the ...
3
votes
2answers
77 views
How to generate a list from an iterator and some arbitrary function
Suppose I'd like to generate a table of integers:
Table[i, {i, 10}]
Great; now suppose I want only the integers that are even
...
1
vote
1answer
64 views
How can I use list processing functions on data in a file?
How might I work with the following functions on a list, if the list is a disk based file?
Partition[]
DeleteDuplicates[]
Split[]
SortBy[]
The file is too ...
6
votes
4answers
210 views
How to apply a function to a list of tuples
trialList = {{0, 24.701}, {1, 24.69}, {2, 24.733}};
f[x_] := x + 1;
I would like to apply the function f to only the second ...
8
votes
4answers
134 views
How to pass a list of arguments into HoldAll
I have a list of arguments (which in reality is lengthy):
arguments = {a, b, c}
arguments2 = {a_, b_, c_}
f[Sequence@@arguments2] := a + b + c
Note: It seems ...
2
votes
1answer
56 views
How to extract the bin width from a Histogram made with an automatic binning method?
I am using the Scott binning method with Histogram and Histogram3D to plot some data. How could I find out the bin width chosen ...
6
votes
1answer
76 views
Position with Except returns first item {0} and last item {}. Why?
Here is a simple list:
l={1, 0, 2, 1, 0, 1, 0, 1, 2, 0, 2, 0, 1, 0, 1, 0, 0}
To get the position of non-zero elements I use ...
4
votes
3answers
154 views
Replace very small numbers by zero in the output of a list
I have a long nested list, but many elements are numbers of order 10^-18 or less, eg
...
4
votes
1answer
90 views
Integrating a list of functions
For the purpose of this minimal example, let's say we have a list of functions, like this:
f[y_?NumericQ] := {NIntegrate[z*y, {z, 0, 1}], a y}
I want to ...
1
vote
1answer
75 views
Syntax for integrating over limits specified by a Table
I wish to use NIntegrate to compute multidimensional integrals. However, I don't want to manually input the limits for the dimensions. I want to store the ...
3
votes
7answers
128 views
Remove elements at certain positions from all sub-lists?
Consider a big list where all the inner lists length's are the same
list = {{x1, y1, z1, t1}, {x2, y2, z2, t2}, {x3, y3, z3, t3}, ...};
elementNo = {4, 3, 2};
...
4
votes
2answers
92 views
How to only work on sublists with non-zero (or positive) values
i have a large compositional dataset which contains non-zero and zero values. here is a sample:
...
16
votes
7answers
809 views
How to Derive Tuples Without Replacement
Given a couple of lists like a={1,2,3,4,6} and b={2,3,4,6,9} I can use the built-in Mathematica symbol ...
6
votes
2answers
135 views
Select elements of list within a date range
I have a list which consists of elements each of which has a date in DateList format, a number and a flag (Y/N). e.g.
...
13
votes
10answers
612 views
Pretty way to group elements at odd and even positions
How to make a function that splits list elements by odd and even positions? Shortest implementation wins. I myself came up with:
...
3
votes
2answers
406 views
Optimize inner loops
I'm Mathematica newbie so please be gentle :)
I have this, heavily non-optimized part of code, which I would like to speed up. I have put all matrices to be RandomReal, but in my code they take ...
1
vote
1answer
43 views
PrependTo fails on a Table of Evaluated funtions
My task is something like this:
PrependTo[Evaluate[Table[{x, Sin[x]}, {x, 0.1, 2 \[Pi], 0.1}], {0., 1.}]]
where I tried also skipping the
...
7
votes
1answer
73 views
Ordering function with recognition of duplicates
Fairly often I have a need to get the Ordering of an expression but with recognition of duplicates. For example:
...
17
votes
3answers
343 views
How to efficiently find positions of duplicates?
Is there an efficient way to find the positions of the duplicates in a list?
I would like the positions grouped according to duplicated elements. For instance, given
...
0
votes
3answers
120 views
How to construct pairs in a list?
I have an expression like this,
input = x[1] x[2]^3 x[5]^2;
Fist step, we can get a list from the input expression,
...
5
votes
4answers
192 views
Prevent Part[] from trying to extract parts of symbolic expressions
If you have a list, e.g.
{1, 2, 3}
then you can extract the $k$th part using Part (...
10
votes
3answers
379 views
What is Mathematica's equivalent to MATLAB's filter function?
The MATLAB code
filter(0.5,[1, -0.5], [1:10])
is equivalent to
Rest@FoldList[(#1 + #2)/2. &, 0, Range[10]]
I don't ...
3
votes
4answers
202 views
Extract function arguments
Is there a way to extract the arguments of a function? Consider the following example:
I have this sum
...
9
votes
2answers
201 views
Speed up 4D matrix/array generation
I have to fill a 4D array, whose entries are $\mathrm{sinc}\left[j(a-b)^2+j(c-d)^2-\phi\right]$ for a fixed value of $\phi$ (normally -15) and a fixed value of $j$ (normally about 0.00005). The way ...
3
votes
2answers
138 views
For loop with steps other than 1
I would like to do a For loop with a jump 2*Pi instead of 1.
For[j = 0, j <= nmax, (incr = 2 Pi), ...]
Actually what I want to do is ...
2
votes
1answer
38 views
Replace a specified portion of an array with elements from another smaller array
This may be a trivial question, but I have been at it for a couple of hours and I have not made much progress.
I have a 10 x 10 array (T) that I have used to generate an 8 x 8 array (Q). I want to ...
12
votes
9answers
325 views
Dropping n consecutive terms from a list periodically
Suppose I have the following list
lis = Range[100];
and I want to remove n consecutive terms periodically from the list. For example suppose I want to drop terms ...
2
votes
3answers
205 views
How make f[{x,y}] evaluate as f[x,y]?
I frequently encounter the situation where I have a function of two real variables defined, e.g.:
f[x_, y_] := 9 - x^2 - y^2
But then I need to feed into ...
1
vote
1answer
107 views
1
vote
2answers
88 views
Subtract more than one array using DeleteCases
I need to create an array subtracting two arrays from another array. I know how to subtract one:
am = DeleteCases[amp, Alternatives @@ af]
I can subtract an ...
1
vote
2answers
123 views
Select rows from table by keys
I am looking for a way to iteratively select all sublists with the same ID (my 1st column, residual columns are AbsoluteTime entries). First, I obtained the list of ...
8
votes
1answer
215 views
How to remove some elements in a list based on a rule?
I want to deal with the following list.
mylist = Table[cof[i] exp[i], {i, 1, n}]; (*n is very larege *)
exp[ ] is a function ...
-8
votes
1answer
198 views
Plotting Energies vs. m for all values of R with the colors of the levels indexed by R [closed]
I have two lists like this:
...
4
votes
1answer
137 views
A Faster way to combine two Lists of different structures into one of a different structure [duplicate]
I have the following two lists (each containing over 500,000 elements). Here is a sample:
...
0
votes
0answers
36 views
Correspondence between eigenvectors and eigenvalues [duplicate]
Let us say I have a matrix h (2x2). Now, I want to get the eigenvectors and eigenvalues of my matrix h:
...
