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

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14
votes
1answer
140 views

Unexpected pattern matching behaviour: PatternSequence vs. Optional

fixed in 10.1 (windows) Consider the following pattern-matching expressions: ...
11
votes
5answers
312 views
0
votes
0answers
51 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
66 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
182 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
160 views

Problem using Position applied on matrix with Infinity elements

Am I doing something wrong here? ...
12
votes
1answer
308 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
56 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
188 views

Pattern Matching in Lists

I have a UN voting dataset – taken from a CSV file – where each row is in following format: ...
1
vote
2answers
158 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
45 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
168 views

LetterCharacter for Cyrillic symbols

Why does the code StringMatchQ["ы", LetterCharacter] return False? Probably because: ...
3
votes
2answers
102 views

Power[__] Pattern works like Level

I came across this case: ...
2
votes
0answers
58 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
85 views

How to ensure efficient order of operations for rules, slots, substitutions?

I need to calculate several functionals Q[[t]] of a pdf f[x]. ...
19
votes
2answers
361 views

What does f_[whoCalled]^:=f really mean?

I came across the following post by John Doty in this Google Groups discussion: On Friday, January 11, 2013 8:23:16 PM UTC-7, amzoti wrote: It is clear the Mathematica uses Lisp as one ...
2
votes
1answer
136 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 ...
10
votes
2answers
212 views

Unexpected result from StringReplace

The following works as expected. StringReplace["xxxyxz", "x" ~~ _ -> "ww"] "wwwwww" And so does this. ...
3
votes
1answer
153 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 ...
1
vote
1answer
61 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: ...
2
votes
3answers
377 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
180 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
556 views

Camel hump string split

Given System names of 2 or more characters: systemNames = Names["System`*"] // Select[StringLength[#] > 1 &] ; Is ...
7
votes
2answers
154 views

How to define patterns to filter lists of replacement rules?

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 ...
1
vote
0answers
256 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
289 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 ...
2
votes
1answer
296 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 ...
2
votes
1answer
45 views

Linear function on strings using UpValues

I have two functions Sup and Sdown that take a string of letters with allowed characters ...
8
votes
3answers
184 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
132 views

Symbolic and numeric calculations (and plots) simultanuosly [closed]

I use Mathematica to do a bunch of symbolic calculations (integrals, ...). This is good because I found that sometimes, if I plug in numeric values, Mathematica takes much longer. However, sometimes ...
0
votes
2answers
83 views

How do I tell pattern searcher the order in which to search for patterns given in general form?

I have a really long sequence of Symbols inside a function, say nonCommute[a,b,c,e,e,f,g,b,i,j], and I am implementing a ...
6
votes
3answers
185 views

Removing non-word characters in certain parts of a string

I would like to ask how I can remove non-word characters from a string, but only in certain cases. I have read this article, so I know how to get the words out of a string. My text is however a bit ...
4
votes
6answers
464 views

Command to take the first elements of a list that match a pattern

I want to find the number of elements in a list in a row that match a certain pattern. So for this list {1,1,1,1,0,0,0,1,1,1} It should return "4" because there ...
3
votes
1answer
205 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: ...
4
votes
1answer
99 views

FreeQ and arguments of Hypergeometric2F1

I was trying to use FreeQ to test for the presence of Hypergeometric2F1 functions in my expressions. I encountered the following ...
2
votes
0answers
100 views

Understanding the order of applying Rule to expression [closed]

I am a little confused about: In what order is a Rule tried to apply to an expression? In a depth-first order or otherwise? For example, ...
7
votes
2answers
293 views

Why doesn't this pattern work?

I want the in-built function Count to count the elements in a list which are greater than a value. Example: ...
3
votes
2answers
175 views

Matching a case when one element in a pair is Null

I've got a dataset of laitutdes and longitudes. Unfortunately, some of the dataset was from when a time when lat/longs weren't constantly recorded. So I need to remove the invalid data before working ...
6
votes
2answers
302 views

Apply Trig Identity to Transform Sum of Sinusoids into Phase-Shifted Cosine Function

I'm trying to solve for the output of a simple RC low-pass filter, with Cos[w t] input. The convolution of the input with the RC transfer function gives me the right output, but I'd like to be able to ...
3
votes
1answer
328 views

Recognizing Matching Colors in a Game Grid from a Camera Image

I am relatively new to Mathematica, having taken my first serious dive into it this week. As a fun project to teach myself some of the basics, I've come up with a goal of optimally solving a game ...
3
votes
3answers
104 views

Pattern for finding matches that are different [duplicate]

I am trying to solve the following problem. I have tuples of size 3 {{a, b, c}, {a, b, c}, {a, b, c}} I would like to find cases where all the elements in a ...
10
votes
5answers
425 views

Repeating Digits

I have written ...
4
votes
4answers
258 views

Sublist pattern matching

Is there any way to simplify the following pattern: {p___, {a___, x_, x_, b___}, q___} :> {p, {a, x, b}, q} Ie. where I remove duplicated elements within ...
5
votes
4answers
240 views

Finding the position of a single array in a list of arrays that contains wildcard variables

Consider two lists: superList = {{wc,wc,1,wc,wc}, {wc, wc,2, wc, wc}, {wc, wc, 3, wc, wc}, {wc, wc, 4, wc, wc}}; littleList = {a,b,3,c,25}; In ...
1
vote
2answers
121 views

text analysis: split document in seperated lines

For a text analysis I want to split a large document in seperated lines. Then I want to calculated for example the average number of words. A example of the document is the following: ...
9
votes
4answers
293 views

Pattern match for nested Association

Suppose I have Association testAssoc=Association[a->Association[1->1,2->2],b->Association[1->1,2->2]] which ...
6
votes
4answers
351 views

Pattern matching - comparing two lists

I would like to compare two different lists to see if the shorter one is a member of the larger e.g. is the list {2,3}, with that sequence of elements, a member of {1,2,3,4,5}? I have tried using ...
6
votes
1answer
332 views

Sentiment analysis of tweets

I want to use Mathematica for a sentiment analysis on tweet-messages. For that purpose i selected several tweets. Each tweet is interpreted by myself as positive (pos) of negative (neg). For example: ...
3
votes
2answers
186 views

Convert matrix rows into variables

Can anyone show me how to set all matrix rows to variables. For example, I have matrix w={{1,2,3},{3,2,1},{0,0,0}} and I need to set each matrix row to be separate ...
1
vote
1answer
97 views

Function returned an unexpected list

I was trying out a question in Wellin's Programming with Mathematica that says the following. Question: Given a set of points in the plane (or 3-space), find the maximum distance between any pair of ...