# Tagged Questions

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

85 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 $(i,j)$...
655 views

...
216 views

### Speed and the MapThread function

Can anyone help explain why MapThread is so slow in this simple case? ...
75 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 ...
279 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 ...
194 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 ...
81 views

### Map function with a counter

How can we embed a counter in the Map function? Consider a data set such as data = {{a, b, c, d}, {e, f}, {g, h, i}}. The ...
129 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 Map[] levels. For example, ...
623 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 ...
91 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 ...
138 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: ...
124 views

### Loop in a loop, or how to evaluate complex expressions

I need to find $h_{0j}$ for every $1\leq j\leq300$, where \begin{multline*} h_{0j} = \sum_{q=1}^{Q}g_qe^{-\lambda_q j\Delta}\frac{e^{\lambda_q\Delta}-1}{\lambda_q} + \sum_{p=1}^{P}\frac{e^{-\alpha_p j\...
60 views

### How to generate commands which are very similar?

I have several data sets that I wish to interpolate and integrate like this: ...
130 views

### A problem with Compile and Map

There is a weird behavior of Compile that I do not understand. Consider the following example: ...
136 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 ...
102 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 ...
360 views

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 ...
55 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 ...
224 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 ...
277 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 ...
208 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 ...
82 views

### Tutorial for Map, Apply, etc

I have this code: ...
138 views

### Misunderstanding the difference between Map Apply (@@@) and Map (/@) [duplicate]

Here's a minimal working example of a problem I'm having: ...
194 views

### MovingMap maps to second level unexpectedly

I'm trying to build a financial indicator in mathematica. I import some historical data ...
104 views

I currently use MapThread[f, {{a1, a2}, {b1, b2}] for obtaining { f[a1, b1], f[a2, b2] }. Is there a version (or alternative) ...
73 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 ...
276 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 ...
150 views

### Fixed Points Problem with 2D Mapping

I have been playing with the mapping given by ...
153 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. <...
405 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 ...
229 views

### Adding map to 3D plot?

I've made a 3D plot of a pressure surface over the region 160W-20W, 20N-80N - the right panel and I would like to put a map under it, probably just continental outlines for simplicity. I'm just ...
73 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 ...
166 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: ...
232 views

### How to use select and map together

I have two lists, list1 and list2. I want to Select from ...
74 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: ...
47 views

### Summimg peculiar nestings

I have some lists with peculiar nestings: ...
303 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 ...
65 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},...}. ...
126 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 : ...
115 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: ...
70 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 ...
96 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 ...
91 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: ...
167 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 ...
122 views

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

Consider an example Dataset: ...
35 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 <...
327 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. <...
122 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....