Questions tagged [map]

Questions about applying functions or operators to expressions, especially constructs that take advantage of Map (/@) functionality.

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3
votes
2answers
120 views

Faster use of Condition for a large array (see the example)

Here is the example/problem. I have a array of $n$ random number. n = 2000; p = RandomReal[{0, 9}, n]; I have to create a $n\times n$ sparse matrix with $(i,j)$...
7
votes
5answers
2k views

How to elegantly map multiple functions over a matrix?

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8
votes
2answers
360 views

Speed and the MapThread function

Can anyone help explain why MapThread is so slow in this simple case? ...
1
vote
1answer
80 views

How-to implement iteration over a result of an iteration in a functional way

I have a pure function f:= #1 * #2 * #3 &; Which I can invoke in a following way: f[#,2,3]& /@ {1,2,3} Which ...
7
votes
2answers
738 views

Applying function to cartesian product of two lists

I have two lists X = {1, 2, 3}; Y = {5, 6, 7, 8}; I want to apply function g[x,y_,z_] to all pairs from X*Y, so I need to ...
4
votes
2answers
207 views

How to convert a list of 3D points to a list of distances?

How do I apply a function (this case EuclideanDistance) between element i and i+1 on a list ...
1
vote
1answer
366 views

Referring to arguments in nested functions

I am interested in executing the following command but don't know the proper syntax to distinguish between nested arguments, here at the Select and ...
20
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2answers
1k views

Can A Plot Be Overlayed With A Map?

Some brief, only slightly important background. I am doing a research project using the data from NASA's GRACE mission. I wrote a short Perl script to take two data files and find the change in ...
3
votes
1answer
892 views

Map with multiple arguments

I have a function f[m,n] and a list of arguments args = {{m1,n1},{m2,n2},{m3,n3},{m4,n4}, ...} that I want to apply to it. I ...
5
votes
1answer
202 views

Map an Argument to a list of functions

I want to "map" an argument to a list of functions. Here is the concrete Problem. I generate a list "Messungfit" of functions: ...
1
vote
2answers
69 views

How to generate commands which are very similar?

I have several data sets that I wish to interpolate and integrate like this: ...
5
votes
2answers
176 views

A problem with Compile and Map

There is a weird behavior of Compile that I do not understand. Consider the following example: ...
0
votes
1answer
210 views

How do I manage my memory better when using the Map function?

So I'm attempting to write a Mathematica program that prints a range of natural numbers as the sum of four cubes. I wrote the following Mathematica code to try this, but am running into a memory ...
0
votes
1answer
202 views

How to switch keys in a Map to Association [closed]

I have an association that has parameters for a function. These parameters represent two cases that need to be applied to the function. Some parameter values are common to both cases but some are ...
7
votes
6answers
670 views

Indexed Map Thread

I'm attempting to MapThread a function of two lists that requires the index of the list values. For example, MapThread[#1*i+#2*j&,{{a,b,c},{e,f,g}}] Where #1 ...
0
votes
2answers
72 views

Different behaviour of Map and Inner in replace rules

Why does x[{1, 2}] /. {x[l_] -> Map[func, l]} {1, 2} not behave as expected, while for example ...
5
votes
3answers
457 views

How to map over inner keys of nested Associations?

Considering an association: <|"a" -> <|aa-> "asc", bb-> "asd", cc-> 0, ImageType -> "asd", dd-> "asd"|>|> How can I make the inner ...
1
vote
1answer
945 views

What is the “proper” way of multiplying a list of vectors by a matrix? Why Map does not work? [closed]

I am an absolute newbie with Mathematica, so please forgive me if this is stupid, but for the life of me I can't solve this. Suppose I have a list of vectors $b_{1...n}$ and a square matrix $A$ and I ...
2
votes
4answers
268 views

Using Map sequentially

I'm trying to simulate the probability of a balanced hand in Bridge (The Theory of Probability by Santosh S. Venkatesh, 2013) using Mathematica. The problem is solved in the textbook but I just wanted ...
0
votes
1answer
99 views

Tutorial for Map, Apply, etc

I have this code: ...
4
votes
1answer
253 views

MovingMap maps to second level unexpectedly

I'm trying to build a financial indicator in mathematica. I import some historical data ...
1
vote
3answers
147 views

MapThread (or alternative) for adding fixed option

I currently use MapThread[f, {{a1, a2}, {b1, b2}] for obtaining { f[a1, b1], f[a2, b2] }. Is there a version (or alternative) ...
1
vote
2answers
79 views

How to change list to a list of points

I have a list of angles {a1, a2, .... , an} and I would like to have a list of points ...
8
votes
5answers
531 views

How to Map a function with HoldAll attribute

First of all, I'm not sure about the title of this question, so please correct me if there is any title more sensible than mine. The problem is the following: I have a function f that checks if a ...
3
votes
1answer
297 views

Fixed Points Problem with 2D Mapping

I have been playing with the mapping given by ...
3
votes
1answer
263 views

Parallel Apply on a deeply nested expression

I have a deeply nested expression, i.e. something like {{{{...}..}..}..}, and I'd like to use Apply in a parallel fashion, e.g. <...
9
votes
3answers
559 views

Functional equivalent of a For loop referring to consecutive elements in a list

I have implemented this function which smooths the values in a list by, if it encounters a zero, replacing this entry by the average of its two neighbours (apart from the first and last values of the ...
8
votes
2answers
178 views

Is there an equivalent to MovingMap[] for functions that work on more than one TimeSeries?

I have a family of functions that require two TimeSeries (A and B). As a trivial example, imagine a function called beta[tsA_,tsB_] that determines the slope of the linear regression line for the ...
5
votes
2answers
245 views

Indexed Thread on dataset and list

I currently have a dataset, and I would like to add a column based on another list. For example: ...
4
votes
2answers
800 views

How to use select and map together

I have two lists, list1 and list2. I want to Select from ...
0
votes
2answers
104 views

How to continuous apply a function to an argument? [duplicate]

In order to calculate x = sqrt(1 + x) for a given number x, 40 times, I tried this: ...
1
vote
1answer
52 views

Summimg peculiar nestings

I have some lists with peculiar nestings: ...
3
votes
3answers
956 views

Use map on a different level

I have just started to get used to Mathematica's Map, Apply, and related functions, and I can't figure out how to do maps that require working "one level down". For example, I am currently trying to ...
0
votes
1answer
125 views

Fastest way to make division between a number and elements in a list [duplicate]

I have a list y={{a,b},{c,d},...} of dimension {10^5, 2}, and number x. I want to divide only the second part of each element of the list by x, and have as result a new list {{a,b/x},{c,d/x},...}. ...
0
votes
1answer
173 views

Superpose a map and a region plot

I would like to add on a map of city a region plot, which is this one in this case : ...
2
votes
1answer
130 views

Why is Nearest not giving me expected result

I have the following list: numbers={0.,0.6,0.8,1.,1.2,1.4,1.8} Then I calculate the midpoints: ...
0
votes
1answer
105 views

Elegant ways of solving this file batching task

There are a batch of data files in a folder (dir = "D:\\Documents\\datadir"), each of which consists of a list of data items, one per line. Each data item is a pair ...
2
votes
3answers
103 views

How to test a condition for a list and output all the expression that is true?

Suppose that I have a list lis={x-y,x+y,x*y}; and a function f[a_,b_]:=#/.{x->a,y->b}& I want to output all the ...
4
votes
2answers
109 views

Count the number of element repeats at various distances

I have a function of x: f[x_] := Abs[Extract[list, x + n] - Extract[list, x]] I then apply this: ...
2
votes
2answers
179 views

How to Map each cell in a matrix to another and solve the system?

tab1 = {{a1, a1 + a2}, {b1, b2*b2}} tab2 = {{2, 5}, {5, 2}} I want to map like this ...
6
votes
1answer
169 views

How can Map be given access to the keys of a Dataset?

Consider an example Dataset: ...
0
votes
1answer
53 views

MapThread with incompatible length (How to Map twice in the same line)

l and b are two lists of vectors with different length. I need the list of vectors that is constructed by adding each member of <...
9
votes
3answers
480 views

Mathematica periodic moving map

I am pleased to have MovingMap in Mathematica 10. But, today, I encountered the problem that needs MovingMap with a periodic boundary condition. To be specific, Consider the following example. <...
2
votes
1answer
158 views

Excluding cases from Map

I'm doing operations of the form: PowerMod[#, -1, 126]+# & /@ Range[1, 125] When a number is not invertible, I don't want it to be included in the result set....
2
votes
3answers
186 views

How to manipulate one column of a table using the value in another column

Let's imagine I have the following table structure data = {{a, b}, {c, d}, {e, f}}; and I want to transform it into the following table ...
3
votes
1answer
45 views

Mapping also for one element (or telling it how to do so if head got changed)

Some code generates a polynomial, and has the form: expr = Plus[a[i],b[i],c[i],d[i]] I need to apply f to each term. To do ...
3
votes
2answers
101 views

Partial application of MapThread

Suppose that I have f[a_, b_, x_] := ... I'd like to create a list of n pure functions ...
10
votes
3answers
475 views

Operate over list of pure functions

I have list of pure functions (All functions are InterpolatingFunction) i.e {{a, b}, {c, d}, {e, f}, ...} and I would like ...
2
votes
3answers
183 views

MapAt a function at specific positions

I'm trying to solve for $p3$ in 3p3-5 = p1 + p2 at positions where p1*p2 == 0: ...
5
votes
1answer
165 views

Mapping over an association producing an unexpected result

The documentation for associations says that the keys of an association are transparent for many operations. Map is one such operation. However, I am confronted ...

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