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

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7
votes
6answers
1k views

Simplifying nested If statements

Consider : list = {100,102,103,99,106,107,104,112} I want to consider, extract only the "big moves" of that time series. In this case the moves bigger then 5 ...
12
votes
2answers
936 views

How do I find the elements in a list that return the highest value for a function?

Suppose we have a list of values and a function f. I want to find which of the elements maximizes the return value of the function in Mathematica. Let call the ...
13
votes
6answers
930 views

Splitting up delimited data in lists

One task that I frequently find myself doing in Mathematica is splitting lists into lists of sublists, using specific elements to define the break-points. This is particularly useful with imported ...
7
votes
2answers
218 views

How can I get the list of dates in the next $n$ years

How can I get the list of all dates from today 21.02.2012 (which is a palindrome) up to say next $n$ years? Then finding the other palindromes are not difficult. I could not find an easy way to ...
2
votes
3answers
3k views

Product of elements within a list

Please Consider : list={{5,2,6},{2,8,3}} I need to get the product of all the element within list : As of now I do this : ...
20
votes
7answers
1k 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 ...
4
votes
3answers
232 views

Transform vector with lag

Say I have a vector $Z_n$ with and I want to transform it into another vector using this formula: $X_t=Z_t+0.7Z_{t-2}$ The problem is that I am not quite sure how to get that $t-2$ lag in there. I ...
9
votes
4answers
1k views

How to sum up subelements of a list of unknown length

I'm simply looking for the {}+{} function for sublist elements of a list: (Parallel sums of elements) ...
9
votes
5answers
364 views

Finding time-series direction reversal of certain magnitude

I'd like to find the points of a time-series that are a certain distance away (in value, not in time) from the previous maximum, which I consider a reversal. For example, for ...
2
votes
1answer
177 views

List of different values which have to be formatted differently

I have a large list of values which – for presentation in my LaTeX document – I need to format. For instance: I have calculated growth rates which I now would like to have formatted in the form of: ...
12
votes
9answers
446 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 ...
3
votes
3answers
2k views

How to change step size of ListPlot

The command ListPlot will plot lists with a unit step. Is there any way to change the step size of this?
5
votes
4answers
235 views

Take off {} using Position []

Please consider : ...
9
votes
3answers
1k views

Most Efficient Way to Calculate the Product of All Items in a List?

Say that I have a list of returns on a financial asset over time and want to know the total compounded return. To get the answer, I need to add 1 to each return and then calculate the product of all ...
14
votes
7answers
1k views

Selecting a sublist based on Length

If you have a simple list of lists as follows: test = {{1, 2}, {4, 5, 6, 7}, {5, 4, 3}} How do you ask Mathematica to return the sublist of greatest length? ...
14
votes
8answers
522 views

How to neatly get the sum of symmetric elements in a list?

The task is to compute symmSum[{a, b, c, d, e, f}] (*==> {a+f, b+e, c+d} *) symmSum[{a, b, c, d, e}] (*==> {a+e, b+d, c} *) My clumsy solution is ...
15
votes
6answers
441 views

How can I remove B -> A from a list if A -> B is in the list?

I have a list of transformations like this: list = {"A" -> "B", "B" -> "A", "C" -> "D"} As this is used to plot an undirected graph with ...
8
votes
4answers
273 views

Check in a series if there exists adjacent values with less than a certain number of missing values

I'm working with a large number of series of different experiments, where there exist a lot of experiments where there are no entries. I now want to draw a sample where there should exist at least ...
17
votes
5answers
2k views

How to Delete Elements from List1 appearing in List2?

I'm new to functional programming of Mathematica and trying to remove one list of assorted elements from another. However I only find functions working with the Index rather than the values itself: ...
12
votes
5answers
565 views

Permutations[Range[12]] produces an error instead of a list

This input: Permutations[Range[12]] Results in this (error) output: ...
18
votes
8answers
1k views

Selectively Mapping over elements in a List

I am using the following code to easily generate a row of images of all eight planets of our Solar System: ...
5
votes
1answer
145 views

Bug in LengthWhile?

Is this a bug or my MMA went insane or I'm missing something? LengthWhile[Reverse@IntegerDigits[1000], # == 0 &] works fine, but with SameQ instead of Equal, ...
23
votes
6answers
1k views

efficient way to count the number of zeros at the (right) end of a very large number

If I want to count the number of zeros at the (right) end of a large number, like $12345!$, I can use something like: Length[Last[Split[IntegerDigits[12345!]]]] ...
17
votes
6answers
751 views

On generalizing Partition[] (with offsets) to sublists of unequal length

The usual Partition[] function is a very handy little thing: ...
11
votes
7answers
2k views

Combination and Permutation

How could I obtain the list of all the groups of 5 numbers taken from Range[12] such that the 2 lists have an empty intersection : ...
10
votes
1answer
1k views

Finding a subsequence in a list

I have a list and I want to find (in this particular case the first) appearance of a any of some subsequences, of possible different lengths. None of the subsequences is a subsequence of each other. ...
9
votes
5answers
2k views

How to find rows that have maximum value?

Suppose if I have following list { {10,b,30}, {100,a,40}, {1000,b,10}, {1000,b,70}, {100,b,20}, {10,b,70} } How to find rows that have max value in ...
9
votes
2answers
682 views

Flatten at a certain level

In an earlier question the brainteasing fourth syntax variant of Flatten was discussed. I see that with ...
8
votes
3answers
903 views

Why don't * and ^ work as I expected on matrices?

For example, this input... {{1, 2}, {3, 4}}*{{1, 2}, {3, 4}} produces this output... {{1, 4}, {9, 16}} and this input... ...
7
votes
4answers
296 views

Unexpected behavior from GatherBy in version 7

I have come across what appears to be a bug in GatherBy. It appears similar to the problem of using Table[Random[], {1000}] in ...
7
votes
2answers
223 views

How to generate Intervals from a given list?

If I have a list list={3,7,4,5,1} how to get the List of Intervals /Ranges result = {{1,3},{3,4},{4,5},{5,7}}
10
votes
9answers
532 views

How to find range in which a number falls, from given list of numbers?

How can one find the range in which a number falls, from given list of numbers? ...
14
votes
6answers
470 views

Elegantly pairing up mismatched lists

HistogramList returns a list of bin boundaries and a list of counts. There is one more boundary than counts, and I'd like to pair them up so I can feed it into ...
16
votes
3answers
747 views

Efficient way to combine SparseArray objects?

I have several SparseArray objects, say sa11, sa12, sa21, sa22, which I would like to combine into the equivalent of {{sa11, sa12}, {sa21, sa22}}. As an example, I ...
24
votes
5answers
4k views

What is the most efficient way to add rows and columns to a matrix?

Say I have a matrix m and a vector v. ...
21
votes
6answers
7k views

How to find the position of elements in a list satisfying criteria

Say I have a list x={2,4,6,8,10} and I want to find out the positions of the elements that are greater than 7. ...
10
votes
5answers
523 views

How do you efficiently return all of a List but one element?

I have a problem that I am working on that requires that I compare several lists of overlapping data points. As I traverse one of the lists, I'd like to only compare those data to the other lists, and ...
13
votes
7answers
625 views

How to use Union on list of lists without sorting them first?

If I do ClearAll[a, d] lsts = {{a, d}, {a, d}}; Union[lsts] I get the expected answer {{a, d}} but if I do ...
19
votes
2answers
681 views

Data Table Manipulation in Mathematica: Step 2

In this previous post (Data Table Manipulation in Mathematica) we find the brilliant suggestion proposed by Leonid Shifrin that allows to select specific rows identified by the header name. I'm now ...
27
votes
3answers
2k views

Data Table Manipulation in Mathematica

I am a statistician searching for an efficient way to select rows or columns from a table of data in Mathematica. Let me pose the question in 2 parts with a SQL-style table of data: ...