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28
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 ...
24
votes
3answers
459 views

Changing Values in an Association using Map

I am trying to change the value of one key in an association based on the value of another key in that association. So if my association starts as: ...
16
votes
4answers
345 views

Make MapIndexed listable

My goal is to apply MapIndexed to every element of a nested list without destroying the arithmetic operations within the elements. For example, let's start with ...
11
votes
4answers
387 views

What's fastest way of defining 10^5 down values?

I want to define isGood[___] = False; isGood[#] = True & /@ list where list is a list of several million integers. ...
9
votes
6answers
307 views

Using MapIndexed only at certain elements of a list

MapIndexed is a very handy built-in function. Suppose that I have the following list, called list: ...
9
votes
2answers
568 views

Scan vs Map vs Apply

I cannot understand the difference between Apply, Scan, and Map. I have tried to play with ...
8
votes
8answers
401 views

How to use Map inside MapThread?

Given this input lst1 = {{a, b, c}, {d, e, f}}; lst2 = {1, 2}; and the goal is to generate this output ...
8
votes
5answers
373 views

Span a function across several consecutive elements in a list

Suppose that I have a list called list. I would like to span an arbitrary function f across specified consecutive elements in ...
8
votes
3answers
544 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 ...
8
votes
3answers
311 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 ...
8
votes
3answers
247 views

finding anagrams

What I'm trying to find are the 4 letter words in the mathematica dictionary that have the most anagrams and the amount of anagrams these have each. But I can't seem to find all the 4 letter words in ...
7
votes
2answers
323 views

Using Map with If

I have an If statement I need to carry out where the result should be a single number for each time the if is executed. What I have at the moment returns a list for each time the If is executed. I ...
6
votes
2answers
400 views

Map a function over the columns of an M x N array

I have a $N \times M$ list of lists, or rather, a list of records and I want to map a function over its columns (e.g. find the mean temperature, age, etc.). Map ...
6
votes
2answers
270 views

Apply function to every element of list regardless of depth

I want to apply a function to every element of a list without taking braces into account (depth level), but with the same form of output. Here is an example : ...
6
votes
3answers
862 views

Mapping a pure function with multiple slots [duplicate]

Here is a pure function with multiple slots: (#1^2 + #2^2)&[3, 4] 25 But how can I map that pure function over lists of values? For example, say I want ...
6
votes
3answers
169 views

Mapping a function over the parts of a deeply nested Array

I have two tensors: tensorS = Array[Subscript[s, #1, #2, #3, #4] &, {2, 16, 16, 19}]; tensorR = Array[Subscript[r, #1, #2, #3] &, {2, 16, 19}]; ...
6
votes
2answers
573 views

Nested Map and Apply

There are some other questions on this topic but I could not get an answer from reading them. What I want to do is use Apply on some of the arguments of a function, ...
6
votes
2answers
214 views

Variable scoping problem when mapping over delayed replacement

This is something that got me curious while I was playing around with Mathematica. Consider the following (contrived) example: ...
5
votes
2answers
240 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. ...
5
votes
1answer
123 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 ...
5
votes
1answer
440 views

nested use of Apply/Map/MapThread in pure functions

1. My main question I have a function with two argument slots. I wan't to apply this function to 2 lists with different length's. I thought in this solution: ...
5
votes
1answer
83 views

MapIndexed stops at levelspec 1 if only the index is passed?

If the function passed to MapIndexed references the first (or data) argument, the following performs as expected: ...
5
votes
1answer
141 views

How can I substitute something using only map?

For example, I have the equation x^2 + y^2 == x*y and I want to apply the rule y -> s*x I can do it easily by ...
4
votes
4answers
114 views

Plot range of a 2-dimensional function as a function depending on one variable

I want to plot a function of 2 variables x and y, for discrete values of y, like: ...
4
votes
2answers
116 views

Is there a built-in function to map a list of heads to a list of data?

Assume that this built-in function is called func. What I want is func[{f,g},{a,b,c}] will return the following result: ...
4
votes
1answer
497 views

Why is there a huge performance gap using Map with more than 100 List entries

im using Map on a List like this: cube= {{1, 1, 1}, {1, 1, 2}, {1, 1, 3}, {1, 1, 4}, ... , {5, 5, 4}, {5, 5, 5}} Mapping the whole List with 125 entries takes ...
4
votes
1answer
220 views

MapThread Alternatives

I want to add two matrices, the first one containing a 2D vector at each position the other one a list of 2D vectors. The 2D vector from the first matrix should be added to each of the 2D vectors at ...
4
votes
1answer
55 views

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

Consider an example Dataset: ...
4
votes
2answers
63 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: ...
4
votes
1answer
93 views

Parallelize[Mapindexed[]], level={-1}? Sal Mangano's 《Cookbook》

It is easy to Parallelize[] Map[] & MapIndexed[], as having been shown in MMA9 Help for ParallelMap[] and Parallelize[]. For MapIndexed[], the default levelspec is {1}. However there are many ...
4
votes
2answers
129 views

Can one use Map during Expand?

Can one Map a simplifying function to the summands of an Expand before fully expanding the expression in question first? ...
4
votes
1answer
157 views

MapThread and Compile

After discovering that MapIndexed cannot be used with compile (see MapIndexed and Compile) I am now trying do implement similar functionality using a combination of ...
3
votes
4answers
332 views

another way to do this mapping of a two argument function

Sorry, I'm just starting to learn mathematica. I have the following two-argument function: h[{x_, y_}] := x ^ y When I do the following: ...
3
votes
4answers
349 views

How to apply a function of several arguments to a list?

I have a list of triplets: list = {{1, 3, 5}, {4, 5, 1}, {4, 9, 2}} How can I apply a function f to the last element of each triplet when f the last and ...
3
votes
3answers
3k views

Map w/ multiple arguments [duplicate]

Possible Duplicate: How do I use Map for a function with two arguments? If I have a function: F[x_,y_,z_]:=x*y*z and I want to call it with several ...
3
votes
4answers
146 views

Correct slot assignment when mapping from different lists using pure function

Given expr = u == a1 + a2 x + a3 y; and uRep = {u1, u2, u3}; xyRep = {{x1, y1}, {x2, y2}, {x3, y3}}; I'd like to generate ...
3
votes
3answers
113 views

Applying a function of several arguments to the rows of a matrix

I have a user-defined function which takes three vectors as input. Suppose that is like this: f[a_, b_, u_] := Total[a*Total[u]^b] Usually I have vectors for ...
3
votes
2answers
254 views

Mapping multiple functions over an array

I am looking for an elegant way to Map multiple functions over an array. My problem looks something like this: Consider a list of functions: ...
3
votes
1answer
345 views

Using Thread or MapThread over multi-level, ragged lists [duplicate]

This may be a rather strange question. I will try to create a sort of minimal working example. Suppose that I have two lists, list1 and ...
3
votes
3answers
177 views

Dynamic application of several polynomials

I know how to get the 'resulting image' (y) from the application of a certain function (f) (here represented as the coefficients of a polynomial) over a certain interval (x): ...
3
votes
1answer
189 views

Issue with ListConvolve

I am a new Mathematica user, learning the intricacies of functional programming. I have issues withe applying a function over a moving list. My function seems to work and give correct results but it ...
3
votes
1answer
42 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 ...
2
votes
2answers
148 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 ...
2
votes
2answers
156 views

Using DeleteCases and Map together

Given: list1 = {{"a",1},{"b",2},{"c",3}} I would like to delete any pair in list1 that does not have a first element that belongs to list2. Example 1: If ...
2
votes
2answers
369 views

Efficiently compute double sum

Is there a "Mathematica Way", like Map or Apply to compute the following double sum? $\sum_{i=1}^{N_1}\sum_{j=1}^{N_2} m_i n_j \, f(\tau_{i} \gamma_{j})$ I have already stored the lists ...
2
votes
1answer
113 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 ...
2
votes
3answers
113 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: ...
2
votes
2answers
89 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: ...
2
votes
1answer
87 views

Can I use Map here rather than Table?

I've got something that works, but it seems like it would be "nicer" if I didn't have to use Table (or For, etc.). I've got 3 Excel files, each with multiple sheets. Each file also has a sheet ...
2
votes
2answers
59 views

Partial application of MapThread

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