Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.

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4
votes
3answers
181 views

How can I improve NumberString?

I would like to test strings to see if they represent numbers. This should include number representations with precision marks and scientific notation. NumberString ...
1
vote
1answer
46 views

How to modify the output result of an evaluation

For ease of notation, I have defined a function, $f$, that defines the permutation of Bosonic particles such that it has the following properties (the form of $f$ is irrelavent for this question): ...
4
votes
3answers
76 views

Extracting subscripts and superscripts

Suppose I have several types of expressions (in some random order) of the form Power[Subscript[g, a], μ] which is $g_a{}^\mu$ ...
0
votes
2answers
55 views

Keep exponents separately

I have the following expressions $g^{ab+cd+...}$ or in the full form Power[g,Plus[Times[a,b],Times[c,d],...]] How to convert this expression into ...
10
votes
1answer
339 views

How to visualize pattern matching process?

I want a function that does the same job like ReplaceRepeated, and can make the matching process visible. I searched the Internet but didn't find any existing code ...
7
votes
5answers
381 views

Calculating weird numbers

A weird number is a number such that the sum of the proper divisors (divisors including 1 but not itself) of the number is greater than the number, but no subset of these divisors sums to to ...
21
votes
5answers
650 views

How can a big table be treated as a database?

I often work with big tables that I want to treat kind of like a database. Here's an example table. ...
10
votes
2answers
494 views

Is there a way to identify a symbolic fraction?

Is there a way to use Head to detect a symbolic fraction? In particular I find, Head[a/b] Head[1/5] Times Rational ...
4
votes
4answers
133 views

Counting subsequences (i.e., patterns) within a list?

I would like to count the number of subsequences in list. Say I have data given by: data = {1, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1}; I would like to count the number ...
4
votes
7answers
407 views

Given a symbolic expression how to find if starts with a minus or not?

I am using a Mathematica function which returns some error term in symbolic form. I needed a way to determine if this term starts with a minus sign or not. There will be only one term. This is to ...
4
votes
4answers
141 views

Cases with Alternatives failed

Consider this list of rules rules = {a -> 1, b -> 2, c -> 3} I'd like to fish some of the rules out of such a list using ...
10
votes
2answers
1k views

Determine whether some expression contains a given symbol

Given a symbol t and an expression expr, how can I determine whether or not the symbol t ...
2
votes
3answers
94 views

Testing for a vector of reals [closed]

Suppose I define: RealVector[expr_]:=VectorQ[expr,NumberQ[#]&&Head[#]===Real)]; Then: ...
1
vote
1answer
69 views

How to use a list of rules as a data set

I have a file of models that I have saved that I want to be able to call in another program to be solved with NDSolve. Can I use ...
5
votes
3answers
422 views

Camel hump string split

Given System names of 2 or more characters: systemNames = Names["System`*"] // Select[StringLength[#] > 1 &] ; Is ...
0
votes
0answers
50 views

“Meta-matching” patterns [duplicate]

The title refers to the general problem of writing patterns to match pattern-containing expressions (hence "meta-match"). Here's an example. In the following rules ...
2
votes
1answer
52 views

What's the pattern that will match a head anywhere in an expression

I'm looking for the pattern patt[head] that will match any expression expr in which head occurs as a head anywhere within expr. ...
3
votes
2answers
133 views

Replace expression, but only “outside” of a function [duplicate]

I have a horrid expression, which is basically a sum of exponents with coefficients. Here's a taste: What I want to do is to replace ks with another expression, ...
2
votes
2answers
100 views
10
votes
1answer
216 views

Orderless pattern matching

The MMA docs state that "In matching patterns with Orderless functions, all possible orders of arguments are tried". Why then does the following not work? ...
0
votes
2answers
43 views

Matching exponents using Cases[]

I have a question regarding pattern matching. Can anyone explain the results i get ? Cases[Table[x^n, {n, 1, 10}], a_^1] Which gives the following result. {x, ...
1
vote
2answers
171 views

Pattern Matching in Lists

I have a UN voting dataset – taken from a CSV file – where each row is in following format: ...
3
votes
1answer
153 views

Making a list of rules from the list of elements

Starting from the list: {f[q1, q2], f[q3, q4], g[q1], g[q2, q3, q4], d[k1 - q1], d[k2 - q2 - q3 -q4]} I would like to get the result: ...
1
vote
2answers
108 views

Pattern Match and Replace Expression involving Pure Function

Let's say I have an expression that in held form contains a pointer to a function. expr = Hold[2*{"FUNCTION1"} + 5]; ...
2
votes
1answer
39 views

Default value behaves differently when used in Function and when used with Cases

Consider this example: Cases[{4, x, 5 a , 6 x}, x_.*a_ :> x] (*{1, 1, 5, 6}*) It is clear that the _. took 1 as a ...
7
votes
1answer
137 views

LetterCharacter for Cyrillic symbols

Why does the code StringMatchQ["ы", LetterCharacter] return False? Probably because: ...
10
votes
2answers
149 views

Unexpected result from StringReplace

The following works as expected. StringReplace["xxxyxz", "x" ~~ _ -> "ww"] "wwwwww" And so does this. ...
3
votes
2answers
86 views
2
votes
0answers
54 views

pattern matching and applying a function, not working as expected [duplicate]

Consider the following code G[x, y] /. a_[b__] -> Total[a @@@ Permutations[List[b]]] I expect it to give G[x, y]+G[y,x] ...
0
votes
1answer
73 views
2
votes
1answer
118 views

How to use slots and patterns to reduce repetitive calculation?

This is kind of complicated... How can we make MMa calculate values of a function before doing multiple pattern or slot substitutions? Answers to similar questions didn't cover the case where the ...
2
votes
0answers
106 views

Is this a bug in NCAlgebra library?

In course of my work with NCAlgebra package for Mathematica, http://math.ucsd.edu/~ncalg/ , I encountered unexpected behavior of replacements. I am using ...
2
votes
3answers
230 views

Mathematica won't plot the a function that is solved from NDSolve

I have used NDSolve to solve for a function (an angle of a triple pendulum), and now I wish to plot the derivative of that function (the angular velocity). ...
1
vote
1answer
48 views

Pattern matching functions of variables

I am trying work with a general operator z[] and later plug in candidate forms for z[]. But pattern matching turns the inside z[] into a constant and can no longer perform operations on it: ...
31
votes
1answer
565 views

Why is StringExpression faster than RegularExpression?

Edit: as noted by Albert Retey the performance difference is only seen when sub expression extraction is performed. If this test is used below the timings are similar: ...
1
vote
1answer
124 views

Finding the index of (x,y) pairs in a list

I have a large list of $(x,y)$ pairs, and I want to find the index of a particular pair in order to extract some data from another array. By way of an example, ...
6
votes
3answers
134 views

Pattern matching: Times[a_] vs Times[a__]

I don't understand why MatchQ[ HoldComplete[Times[3, 2, 2]], HoldComplete[Times[a_]] ] is returning True. I thought that ...
1
vote
0answers
118 views

Crosscorrelation for nonperiodic signals

I want to detect patterns (of an absorption spectrum which is nonperiodic) with Mathematica automaticly. I have found CorrelationFuncion but as far as I understand, ...
3
votes
3answers
222 views

String pattern defined by number of characters

I want to extract non-overlapping substrings from strings with only four possible characters a,b,c,d. These strings will always have equally many "a" and "d" characters. The substrings x I want satisy ...
4
votes
1answer
55 views

How to define patterns to filter lists of replacement rules? [closed]

I have a list of replacement rules like list˘of˘replacement˘rules = {a -> 1, b -> 2, c -> 3} and I want to filter all the elements where ‘b’ is replaced ...
8
votes
1answer
220 views

Transformation rule on a list of non-negative integers

I am trying to create a transformation rule that takes a list of non-negative integer values of any length, finds a non-zero entry in the list, adds 1 to all preceding numbers, subtracts 1 from the ...
15
votes
3answers
468 views

Grabbing a number of characters around a string pattern

If I have some string data: text = StringTake[ExampleData[{"Text", "DeclarationOfIndependence"}], 400] "When in the Course of human events, it becomes ...
6
votes
3answers
181 views
2
votes
1answer
70 views

Deleting empty cells and selecting cells matching a pattern

Is there any way for me to automatically select all cells that are completely empty? You know, those cells that you create but end up cutting what's in them and paste it somewhere else, so after a ...
14
votes
5answers
706 views

Getting number of binary digits combinations without “forbidden” patterns

I need to get the number of all combinations of binary digits in an 8-digit binary number, but not including those that follow some "forbidden" patterns like these: ...
2
votes
1answer
36 views

Linear function on strings using UpValues

I have two functions Sup and Sdown that take a string of letters with allowed characters ...