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

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34
votes
6answers
2k views

Find zero crossing in a list

I'm looking for a function that finds the index of the zero-crossing points of a list. Before I go making my own subroutine to do this, I was wondering if anyone knows of any built-in Mathematica ...
9
votes
2answers
2k views

How to get Matlab data imported with the same dimensions?

I have some Matlab image data with the following dimensions (output is from Matlab): >> size(im) ans = 86 86 3 45 The data imports just fine ...
6
votes
1answer
376 views

Count sublists which match pattern

I have a list which looks like this: data={{12,0},{0,0},{20,1},{0,0}, {0,-1}}. Now I would like to count the number of sublists which: have both slots zero the ...
2
votes
1answer
149 views

How to arrange elements of a list

A file consists out of (x,y,z) data and I need the z-values arranged like this: {{z[1],z[2],...z[idimx]},{z[idimx+1],z[idimx+2],...z[idimx*2]},{....}} With ...
15
votes
6answers
1k views

Best way to extract values from a list of rules?

Mathematica has a lot of list manipulation functions, and, also because I don't work with lists often, at times I'm a bit lost. I'll find a way, but I'm sure it's not the most efficient. Case in ...
5
votes
6answers
358 views

How to change specific values in a List [duplicate]

In a list lst I want to change all values > 255 to 255. Why is this code not working? ...
4
votes
2answers
287 views

Mathematica list element sort

I have a list, say, ...
18
votes
11answers
1k views

Generating an ordered list of pairs of elements from ordered lists

I have a pair of ordered lists. I want to generate a new ordered list (using the same ordering) of length n by applying a binary operator to pairs of elements, one from each list, along with the index ...
2
votes
2answers
151 views

Comparing elements of the $n^{\text{th}}$ sublist in a ragged list with the $n^{\text{th}}$ member of a sequence

I have a list of lists that are not of the same length (for example, {{6}, {14}, {6, 26, 30}}), but I have to compare every element in the $n^{\text{th}}$ sublist ...
4
votes
1answer
147 views

MapThread with several cells as output

Assume I have defined the following function: FF[{x_, y_}] := {x^2 + y^3, 3.5*x*y} I would like to apply FF on a list of ...
17
votes
8answers
551 views

Applying And to lists of Booleans

I'd like to take {True,True,False} and {True,False,False} and apply And to get ...
1
vote
1answer
104 views

How can I manipulate with elements inside sublists if sublists of different lenght?

I have some kind of output like this: {{1, 5}, {1, 13}, {1, 5, 25}}. I would like to be able to enter in each sublist and make sums of every two elements in sublists, for example my desired output ...
3
votes
2answers
95 views

How to uncompress only the compressed elements in a matrix

I have data in a rectangular structure – something like matrix={{a,b,c},{d,e,f},{g,h,i}}. The problem is that some of the columns consist of uncompressed data and ...
5
votes
6answers
314 views

Creating sums of elements from a list

I have a list $(d_1, d_2, .. d_k)$ and I want to create all sums that I get for adding only two elements for my list $(d_1+d_2, d_1+d_3,...d_{k-1}+d_k)$. The ...
13
votes
7answers
367 views

Get the first element after the first sequence of length N of consecutively increasing values

I'm looking for an efficient way of extracting the first element after the first sequence of N consecutive elements in which the values are increasing. If these are the data of a toy example: ...
7
votes
7answers
422 views

How to pick an element of a row corresponding to the minimum in a particular column?

How can I find what value in column 1 of my list corresponds to the minimum value in column 2?
3
votes
1answer
169 views

Efficiently keeping elements in a list (an input list) that exist in another list (a keep list)

I have some code that generates lists of integers (one such list is called, for example, inputList). I also have a "master list" of integers that should be kept, ...
1
vote
2answers
197 views

How to arrange a list on a triangular pattern?

I've made a multiplication table with this: Then I removed the repeated permutations with: gg = Range[1, 10]; Subsets[gg, {2}] // TableForm Now, when the ...
11
votes
4answers
291 views

Thread a function over a list and with a non-atomic 2nd parameter?

From the documentation, Thread's behavior on functions where the first parameter is a List and the second is an atomic expression, is this: ...
1
vote
2answers
226 views

Symbolically associate vectors and their norms

I am wondering how to handle the following situation: I do have vectors of known dimension that I would like to handle symbolically. I suppose I can do something like ...
11
votes
2answers
1k views

Sorting a list with secondary criterion

Is there an easy way to sort a list on multiple levels of criteria? By this I mean, first the list should be sorted according by criteria A (the same as using the usual sort function, ...
9
votes
5answers
330 views

Finding first instance of a relationship between elements in two lists

Suppose I have two lists, say: A = {1,5,10,200,50,7} B = {4,3,19,78} For each element in A, I would like to find the index of the first element in B which ...
27
votes
12answers
1k views

Map a function across a list conditionally

It seems that this is a really basic question, and I feel that the answer should be obvious to me. However, I am not seeing. Can you please help me? Thanks. Suppose I have a list of data ...
5
votes
5answers
915 views

Replace values which obey certain criteria

I'd like to replace all values in a list which obey one or more criteria with another value. Example: Replace all values>30 by 30. data={{3,35},{2,7}} ...
21
votes
3answers
792 views

Emulating R data frame getters with UpValues

What's the best way to emulate R's data frames functionality? This includes the ability to select rows and columns in a 2-dimensional table by the string identifiers positioned typically in the first ...
2
votes
4answers
355 views

Building a list recursive with one or more arguments

Consider the following: data={a,b,c,d}; res={{a,b,c,d},{b,c,d,e},{c,d,e,f},{d,e,f,g}}; The idea is to define a function ...
13
votes
6answers
2k views

Counting negative values in list

I would like to count the negative values of a list. My approach was Count[data, -_] which doesn't work. How can I tell Mathematica to count all numbers with ...
7
votes
2answers
327 views

find subsequences of constant increase

A list like l = {0, 1, 2, 3, 4, 5, 7, 9, 12, 13, 18, 19} may have subsequences of constant increase, $a_{n+1} = a_n + k$. For example: ...
9
votes
1answer
188 views

Map efficiently over duplicates in list

I am interested in mapping a function, f over a (long) list which contains duplicates. Since this function takes a while to evaluate I would like to make use of ...
7
votes
3answers
484 views

how to efficiently apply function to all pairs of a set (and collect the results)

To build a graph, I need to apply a function f[a_, b_] to all pairs of a list (3500 elements). The function itself returns a link ...
3
votes
4answers
173 views

Building intervals

I'm facing the right know the problem of building intervals to an arbitrary number. The special thing is that the first and the last intervals should have fixed length, while the "middle" ones should ...
1
vote
2answers
160 views

Using patterns in ReplaceAll to extract elements from tuples at arbitrary depths

Please consider the following: I need to extract from MyList all last parts of each 3-tuple. ...
4
votes
2answers
225 views

Simpler way to repeat an execution with 2D points?

q has the coordinates of quadrilateral. I can get the output below with brute-force but I want to find a simpler solution, perhaps something like f<-q[[1;;2]]. ...
1
vote
1answer
219 views

How can I permute a multiset?

I have a multiset {1, 3, 3, 1, 2} and would like to randomly permute the classes like so: {2, 1, 1, 2, 3} or {3, 2, 2, 3, 1}, what is the simplest and most efficient way to do this? In reality the ...
7
votes
1answer
426 views

Very fast way to do a coordinate frame transform

I need a function that rotates and translates a huge amount of line segments. For example, I have a set of line segments in the form {{x0,y0,z0},{x1,y1,z1}} ...
3
votes
2answers
246 views

Creating a Nearest function programmatically

I've been trying to work out how to create a Nearest function programmatically. My goal is to produce something similar to this, a hand-assembled function: ...
-5
votes
3answers
397 views

Constructing lists by applying functions to another list

Suppose f is a function of two variables: $f = f(x,y)\quad$ and $L$ is a list. Could someone help me in defining a list of the form: $D = \{f(x,y)\ |\ x \in L,\ y \in L\}$ I tried this: ...
12
votes
4answers
297 views

The gap between MapAt and ReplacePart for 2D data tables with headers

Consider a relational table derived from survey data, where each column ("001-01" ...) represents a responder and each row (...
8
votes
2answers
154 views

Behavior of Inner depends on List dimensions?

Consider the following case: ...
3
votes
1answer
156 views

splitting a list into files

Given is a list with x, y, z coordinates: {{100, 94, -1.112}, {100.05, 94, -1.112}, {100.1, 94, -0.982}, ..., {100, 94.25, -1.112}, {100.05, 94.25, -0.855}, {100.1, 94.25, -0.728}, ..., ...
10
votes
3answers
345 views

Generating Linear Extensions of a Partial Order

Given a set $S$ and a partial order $\prec$ over $S$, I'm looking for a way to "efficiently" generate a list of linear extensions of $\prec$. Suppose the partial order is given by a ...
5
votes
2answers
252 views

Creating a list of PopupMenus that dynamically update an element in a list

So as the title says I am trying to make a list where each element is determined by a users choice of an element in a PopupMenu. My first attempt: ...
1
vote
1answer
406 views

Fastest way to sum pairwise potentials

I've been writing a function to sum a pairwise potential on two lists, i.e. two charged bodies, each containing N >> 1 and ...
20
votes
5answers
710 views

MapThread over sublists of different length

I have a list which looks like this: l={{1,0,3,4},{0,2},{0,0,1,3},{1,2,0}}. Now I would like to count how many 0s the sublists contain in the first, second,... ...
12
votes
2answers
931 views

How do I split up a curve into segments of equal length?

I have a curve that is defined as f[x] and what I'm attempting to do is to divide the curve into equal straight lengths for a number of segments of my choosing that I've defined as nSeg. I've created ...
3
votes
2answers
230 views

Using the elements of a subset in a Do loop

I would like to use the elements of Subsets in a Do loop. I have: ...
3
votes
3answers
251 views

Incrementing a nested list element

I've been wanting to increment a nested list element of which I know the "coordinates". I thought of the following procedure, using Apply with Part. ...
7
votes
3answers
508 views

Specifying string patterns in DeleteCases

It seems that DeleteCases is not compatible with string patterns, at least directly (see, for example, this question). Is this true? If so, why is this the case? ...
4
votes
2answers
250 views

Access pairs of vectors, rather than the matrices, in partitioned data structure at a levelspec

I have some old code to analyze correlation between 2 time series by looking at windows of different lengths shifting across the time series data. The code: gets 2 sets of time series data (in ...
5
votes
3answers
441 views

position of sequence of elements in list [duplicate]

Possible Duplicate: Finding a subsequence in a list Question The position of {3, 5} is the list {1, 3, 4, 3, 5, 5, 1} is 3. How can such a position ...