Questions on correct (or improved) formulation of Mathematica code to achieve particular results. Use this tag (not "symbol") for questions about all those odd @@ /@ # & and ~ characters.

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11
votes
3answers
196 views

Why can't I use Sequence to perform a Select like task? [duplicate]

Suppose I wanted to write down a list of $p^2$, for $p$ a prime between $1$ and $20$. I would expect Table[If[PrimeQ[k], k^2, Sequence[]], {k, 1, 20}] to work. ...
11
votes
1answer
282 views

Infix form of PutAppend ( >>> ) does not work with variable

I'm new to Mathematica, so I suspect this question involves either a misunderstanding involving variables or the usage of >>>. On a webMathematica page ...
11
votes
2answers
1k views

Flatten at a certain level

In an earlier question the brainteasing fourth syntax variant of Flatten was discussed. I see that with ...
11
votes
1answer
218 views

Extract what symbol is set by SetDelayed, Set, TagSet, UpSet, SetAttributes, etc

One of the recent features of the Mathematica Plugin for IntelliJ IDEA (www.mathematicaplugin.halirutan.de) is a Structure View which let's you see information about several definitions that are done ...
11
votes
1answer
144 views

The equivalent of dplyr mutate with Dataset

In R, there is a package "dplyr" that works on data.frame objects, which is one of the origins of the Mathematica Dataset construct. One of the things dplyr can do is "mutate" the columns of a ...
10
votes
4answers
495 views

Extracting equations from Piecewise expressions

Say I have a PDF: PDF[LogNormalDistribution[1.75, 0.65], x] Calculating it, Mathematica gives me an expression that looks like this: I want to extract the ...
10
votes
2answers
388 views

Functions that remember their values

Can someone explain what is going on with the following ... func[y_] := func[y] = (Print["Hello world !!!"];) func[1] Hello world !!! ...
10
votes
3answers
349 views

Why does ++++x return an increment of 2 when the value of x is only incremented by 1?

This line returns 3: x = 1; ++++x However, the value of x after the increment is only ...
10
votes
1answer
679 views

Explain a Mathematica winning one-liner

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10
votes
3answers
793 views

What is the right way to construct DynamicModule

When I'm creating DynamicModules for CDF purposes I'm usualy basing on my experience with that, particular goal and content rather than on deep insight. I want to ...
10
votes
1answer
789 views

What is the difference between prefix/postfix notations and map?

I am new to Mathematica and just experimenting with the different programming constructs. I have been looking at Map and how to evaluate a function for a list of ...
10
votes
2answers
106 views

Functions in a different context are replaced with infix forms of their namesake in System`

So, in an attempt to help out Fabian with his question, I did what I often do, and created a new symbol in the Pillsy` package that I could play with. Since it was ...
9
votes
5answers
5k views

Notation of partial derivative

I want to write partial derivatives of functions with many arguments. Why is it that when I type f[x,y] ctrl+6 (0,1) it turns out to be bad syntax? The output of ...
9
votes
1answer
169 views

Accept Infinity as an Integer argument

I have the following function, albeit contrived: Foo[x_Integer] := Module[{i}, i = 1; While[i <= x && i <= 10, i++]; i - 1 ]; I am ...
8
votes
3answers
2k views

Using D to find a symbolic derivative

I need to do the following: Define a function Take the derivative of this function and have a look at the symoblic representation Substitute in some values With the bonus that I want to use the ...
8
votes
4answers
708 views

Error when using rule as a list index - { i, x[[i]] } /. i -> 5

I can't seem to use a rule to index a vector. x = Range[10]; { i, x[[i]] } /. i -> 5 I get the following error when evaluating the above code, even if the ...
8
votes
5answers
932 views

can the color in MeshStyle be specified by a ColorFunction, such as “SunsetColors” for example. If so, what is the correct syntax?

This is an example given in Help: Plot3D[Sin[x y], {x, 0, 3}, {y, 0, 3}, MeshStyle -> Gray] Could this be changed to something like ...
8
votes
3answers
537 views

how to read in a file in the same directory?

Now I am writing a small package. I have written several files and put them in the same directory. And some files need to read in or include another file in the same directory. But when I simply write ...
8
votes
2answers
3k views

How to reverse the direction of the y axes

I have a similar question to this one. Unfortunately, the answers there didn't help me. I would like to plot a simple function with the normal Plot function. ...
8
votes
2answers
293 views

Cases[data,Colon[key,_]] vs. Cases[data,key:_] toward XPath, XQuery

Exploring methods to index and search tree-structured key:value pairs via named-entity index (key paths) as opposed to Position-based indexing. Using Rule as ...
8
votes
1answer
165 views

Invalid Symbol Characters

What unicode characters are invalid as a Symbol name? Ideally I'm looking for a complete list. Here is the current list ...
8
votes
1answer
484 views

Setting the DifferenceOrder Option

I've been playing around with Method in NDSolve[...] and can't quite seem to figure out how to force ...
8
votes
1answer
113 views

Does the syntax coloring I see indicate a real problem?

I need a behaviour provided by: x = 2; Block[{x = HoldForm[x]}, x] x FrontEnd marks ...
8
votes
1answer
346 views

Treat all variables as local in a module [duplicate]

In most languages, any variable defined inside a function is considered local. ...
8
votes
1answer
167 views

Different behaviours of Default Argument

I don't really understand the behaviour of Default Argument. If I execute this command in Mathematica: In: {f[a], f[a + b]} /. f[x_ + y_.] -> p[x, y] ...
8
votes
0answers
84 views

Syntax error in debug mode

Bug introduced in 8.0 and persisting through 10.3.0 It appears that in debug mode, the \[Piecewise] symbol and its associated grid give a syntax error. For a ...
7
votes
5answers
377 views

Is it possible to insert arguments into functions when they're used like Function@ or //Function?

Is it possible to insert arguments into functions when they're used like Function@ or //Function? Sometimes I need to do this, but then I have to return to the standard function usage: Function[] ...
7
votes
4answers
7k views

Mapping multiple parameters of a function to specific values

I am a little bit confused by the documentation for Apply (@@). I want to define a list of parameters, for instance: ...
7
votes
3answers
4k views

Matrix Multiplication in context of row and column vectors

I've been looking at some matrices in Mathematica and I've noticed something very weird: They're extremely temperamental when it comes to dot products! For example, if I have the following, ...
7
votes
2answers
264 views

Internal Representation of ?name and ??name

Code FullForm[Hold[?name]] Syntax::bktmcp: Expression "Hold[?name]]" has no closing "]". Syntax::sntxi: Incomplete expression; more input is needed . Question ...
7
votes
3answers
333 views

Why can't D[] be used in place here? [duplicate]

Possible Duplicate: General::ivar is not a valid variable when plotting - what actually causes this and how to avoid it? Beginner question: Why can't I use ...
7
votes
2answers
332 views

What's the purpose of the Unique function?

As the title says: What's the purpose of Unique? I understand that it generates some unique symbol, but when and for what is it to be used? Are there applications ...
7
votes
4answers
194 views

How to select only NotebookObjects that are referring to ordinary notebooks? (not palettes etc.)

There is of course function Notebooks[] But, unfortunatelly it hasn't got useful options in this context. My question is how to pick ...
7
votes
2answers
879 views

Evaluating an If condition to yield True/False

I would like to decide whether an option passed to my custom function has the value Automatic or something else. This is my attempt: ...
7
votes
2answers
187 views

“A number in base b” and pure functions: why doesn't b^^# & work?

Why do the following not work (in Mathematica 7)? 2^^ # & /@ {1000, 1101} and 2^^ # & @ 1101 This does work: ...
7
votes
2answers
262 views

HoldForm[Operator ##] on some list

Recently in response to this question Mr.Wizard suggested an unusual way to summing numbers. This doesn't seem to be documented. ...
7
votes
1answer
688 views

What does ` symbol in ClearAll[“Global`*”] mean?

I have found an example for clearing all symbol definition by: ClearAll["Global`*"] But what does the symbol ` mean? It isn't the apostrophe ', yet it is not ...
7
votes
1answer
200 views

How can I specify a numerical order for variables?

I need to specify that a variable is less than another, and greater than yet another, in a Mathematica program, because I will later apply a test to them that will determine what functional form to ...
7
votes
3answers
124 views

Morse Code Spacing

Trying to make a function to convert text into morse code and play the sound. Have it pretty much completed, but I cannot get mathematica to emit no sound so I can have a pause between the dots and ...
7
votes
3answers
77 views

TagSetDelayed on a function with a delayed value

I'm trying to automatically optimize cases when the user evaluates Length[returnsList[x_]] to instead use returnsLength: ...
7
votes
1answer
141 views

What kind of creature is h[c] for definition h[c_][x_] := (* function of x and c *)

To implement "Hero's Method" for approximating $\sqrt{c}$, one iterates the function (x + c/x)/2 for a given number c (e.g., ...
7
votes
2answers
476 views
7
votes
0answers
174 views

What is a good way to code long, complex, compilable algorithms?

The functional paradigm of the Wolfram Language used in Mathematica is all around wonderful. For intense numerics, Mathematica comes with the ability to Compile ...
7
votes
0answers
433 views

Do any mainstream text editors support Wolfram Language syntax for highlighting? [duplicate]

Syntax Highlighting for Mathematica on a Blog There is the above, but I'm not terribly excited to install rogue packages. For example on github, I share lots of Mathematica code. I see no way to ...
6
votes
6answers
888 views

Can't comment strings with '*)' inside it

I believe it's a bug in notebook's comment parser. I can't comment strings with *) inside it. Something like: ...
6
votes
2answers
469 views

Splicing a list of arguments into a function with Sequence

Not sure if this has been asked, but I have a fairly simple operation that I don't know the syntax for. Say I have an array with some values, and a function f that accepts an arbitrary number of ...
6
votes
3answers
541 views

Syntax for prefix mode with multiple arguments using @ shorthand

Is it possible to use the @ symbol with multiple arguments? The Prefix command suggested not. If so, why?
6
votes
3answers
301 views

How can I create currying functions using pure function syntax?

For example how can I write In: pureFunctionSyntax[myF] /@ {7, 3} Out: {myF[7, Log[7]], myF[3, Log[3]]}
6
votes
3answers
330 views

Where did I go wrong with my implementation of the trapezoidal rule?

One method for doing quadrature, called the trapezoidal rule, improves accuracy by connecting the points on the curve corresponding to the points of subdivision with line segments, forming trapezoidal ...