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

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-1
votes
1answer
372 views

variable sized lists and using lists as variables

I am trying to scan a parameter space of varying numbers of parameters subject to some constraints (I am interested in any number of constraints just out of curiosity, but in reality no more than 2 ...
8
votes
2answers
398 views

Handling vector comparisons in “Piecewise” function

Is it possible for the Piecewise function to process a vector comparison? For example, my input vector is x={0,1,2,3,4} I would like to define a function that ...
19
votes
2answers
1k views

Extracting values from nested rules in JSON data

I have been using Mathematica to analyse some data from the StackExchange API. It is conveniently available in JSON form, which Mathematica interprets as replacement rules. However, some of the rules ...
2
votes
1answer
159 views

Issues with a Counter that is tallying term appearances

I am working with an array of textfiles, trying to see how frequent certain terms are. However, I am running into some difficulty with my running counts of bigram frequency. Here is a snippet of my ...
10
votes
1answer
538 views

Modifying a List in a function in place [duplicate]

An example will be most specific: func[list_, column_] := list[[All, column]] = Map[#*2 &, list[[All, column]]]; This throws errors. I want to avoid doing ...
8
votes
4answers
267 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 ...
4
votes
2answers
291 views

Why can't NumberQ be used as the head of a pattern?

Consider the following: list={1/First[{}], 1, 2, 1/First[{}], 3}; DeleteCases[list,_NumberQ] I wanted to remove all cases, which did not match ...
15
votes
6answers
1k views

Max of a table/list with indeterminate values

Suppose I have a Table: tab = {1., 2., 3., Indeterminate} When I type Max[tab] I get ...
10
votes
3answers
287 views

How to “ignore” an element of Map or MapIndexed

Say I have some function that I'm applying every element in a list to... if that element matches some criteria: ...
2
votes
2answers
284 views

MapThread on a nested Map

A simple problem I am facing is here: ...
4
votes
1answer
483 views

How do I treat elements in a list as variables inside a module?

I want to be able to assign values to a list element inside a module. For example if I have: ...
9
votes
4answers
270 views

Make a ragged list rectangular by trimming instead of padding

I have a ragged list ragged = {{a,b,c,d,e},{x,y,z}} that I would like to trim (on the right) to be rectangular. The desired result is ...
9
votes
6answers
2k views

extract values from replacement list

Solve returns a list of replacement rules In: Solve[x + y == 3 && x - y == 6, {x, y}] Out: {{x -> 9/2, y -> -(3/2)}} I am only interested in the ...
8
votes
5answers
358 views

How to distinguish between lists and values?

I have a (hopefully small) problem with some numerical integration algorithm, more specifically I want to integrate the imaginary part of a complex valued function, e.g. ...
12
votes
7answers
666 views

Equating matrices (or higher order tensors) element-wise

Say I have two matrices (or, as in my case, higher order tensors) $A,B$, and I want to solve the equation $A=B$. To do so , I need a list of equations that equate entry-wise the elements of $A$ and ...
13
votes
4answers
695 views

Constructing a list that includes a leading zero (01,02,03 … 55, 56, etc.)

I am constructing a list for use in file operations. Say I want to create list which contains values from 01 to 87. The kicker is that the first nine integers need ...
6
votes
2answers
202 views

Operate on several lists to create one list

How do you put corresponding values from different lists together according to some operation? E.g. I have three lists giving the velocity in the x, y and z direction respectively. I'd like create ...
9
votes
5answers
248 views

Fill out blanks with a upcoming number in a list?

I have a bunch of arrays looking like this: {"", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", ...
2
votes
2answers
2k views

Creating Lists From Loops

Consider the following: lists = Import["G:/Notebooks/Lists.csv"]; col7 = lists [[All, 7]]; For[i=0,i<101,i++,Print[Count[col7,i]]] This will get a 100 cells ...
4
votes
1answer
197 views

What's the most intelligent way to store the information of a selfmade graph?

I have a very long list of element, say $a1,a2, a3$,..., and they are all connected in that each is the child of many parents. E.g. $a74$ is associated with $a2,a55,a71$, and also contains ...
4
votes
1answer
284 views

Defining a string based sort function

I'm having a bit of trouble figuring out the right Sort syntax to use on a list of lists. Consider the following list: ...
4
votes
1answer
358 views

Deleting parts of a large list

At present I am running an analysis on economic data. Within the data I was able to identify countries which went through recession. I then calculated for example the average decline rate of GDP ...
16
votes
1answer
323 views

Are there advantages to using additional arguments of common functions rather than alternative ways of calculating with lists?

(Apologies for the long question title.) One of the interesting, if sometimes confusing, things about Mathematica is that there is always more than one way to do things. Even intermediate users can ...
10
votes
4answers
683 views

Efficiently Visualising Very Large Data Sets (without running out of memory)

I have put a few really hard problems in combinatorics up against Mathematica 8. I'd have to say that it works really well, until you want to view the data. If you look at my question Advanced ...
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 ...
15
votes
4answers
1k views

What is the right way to rotate an array?

Suppose I have an array, not necessarily square: a = $\left( \begin{array}{ccc} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{array} \right)$ I want to rotate it like one ...
2
votes
1answer
230 views

Conditional Data Selection, efficiency

Building up on the solution proposed here : Simplifying nested If statements You can find here the data set : allGazes.dat ...
3
votes
1answer
583 views

How to create a histogram of annual events, such as cherry blossom time

I have calculated blooming and ripening times for a specific variety of plant, based on actual temperature data from over 40 years. I would like to create two histograms on a single axis; one for ...
11
votes
2answers
816 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
904 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
217 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 : ...
12
votes
9answers
444 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 ...
19
votes
6answers
6k 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. ...
4
votes
3answers
228 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
5answers
357 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: ...
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
232 views
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? ...
9
votes
3answers
920 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 ...
13
votes
4answers
373 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 ...
16
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: ...
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. ...
5
votes
1answer
141 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, ...
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 : ...
9
votes
2answers
651 views

Flatten at a certain level

In an earlier question the brainteasing fourth syntax variant of Flatten was discussed. I see that with ...
10
votes
5answers
517 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 ...
14
votes
6answers
455 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 ...