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

learn more… | top users | synonyms (1)

13
votes
1answer
564 views

How to Combine Pattern Constraints and Default Values for Function Arguments

EDIT: As several respondents have noted in the answers and comments below, the original example had a default value that would never be used because of the way patterns and default values are ...
6
votes
2answers
196 views

Is it possible to use PatternTest and Optional value on one Pattern simultaneously? [duplicate]

Possible Duplicate: How to Combine Pattern Constraints and Default Values for Function Arguments First a simple example: define a function "add" with two arguments, and its second argument ...
7
votes
1answer
195 views

Is it possible to specify a context-sensitive, “depth-agnostic” rewrite rule?

I'm using the term "depth-agnostic" in this post to describe structural patterns featuring a "target" sub-pattern that can occur "at any depth" relative to one or more "context" sub-patterns. As a ...
3
votes
2answers
90 views

Pattern matching not going over a list when using default values

if I execute the following command in Mathematica: {a,a^2,a^3}/.a^(n_:1)->b^(2 n) Mathematica returns: {b^2,b^4,b^6} ...
1
vote
3answers
511 views

How do I combine the data from two tables according to a rule of my own devising?

I have two matrices a = m x 5 and b =m x 5 (m is large, say 1,000) which are already sorted as below: How to generate a new matrix c = m x 5 which consists: Column 1: exact replica of Column 1 ...
-1
votes
2answers
259 views

Correct way to compare arrays and do conditional evaluations

I would like to compare two arrays a=: and b= and get: using: (b/.(b_?Positive->a+b))//MatrixForm but this doesn't seem to work? Can ...
1
vote
2answers
242 views

How to generate patterns by a list of integers

I have a list of integers {3,4,2,2}. This list will give patterns {x_,_,y_,y_,_,_,z_,z_,w_,w_,x_} and ...
13
votes
3answers
333 views

Make mathematica treat $e_i^2$ as numeric

With NumericQ[symbol] = True, I can declare that a symbol is numeric. I want the expressions matching: $$e_{\text{i$\_$}?\text{IntegerQ}}^2$$ to be treated as ...
8
votes
1answer
153 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 ...
0
votes
1answer
142 views

Why does “Pattern(1,0)[w,_]” show up in the resulting expression of a differentiation? [closed]

I would like to differentiate the function s, and be able to evaluate it for different w afterwards. I tried the following: ...
8
votes
2answers
352 views

How to Enable Syntax Coloring of Pattern Match Variable Only (i.e. Without Coloring any Associated Pattern)?

Syntax coloring for the following function definition foo[x_List] := ... will color green (and italicize by default) the argument name ...
3
votes
1answer
121 views

How to make a pattern to change x^(2/y) to (x^2)^(1/y) for any x and y?

This might have been asked before. Please let me know if it is. I was looking at an interesting Mathematica question in students forum and trying to solve it, and a chance to learn more about ...
1
vote
2answers
139 views

A function that only evaluates on lists of pairs [duplicate]

Possible Duplicate: Why doesn’t PatternTest work with Composition? I'd like my function to only evaluate when the argument is a list of pairs. It seems like ...
4
votes
2answers
165 views

How to use Optional as an omissible parameter in pattern-match?

Below is a function intended to test if an expression is a polynomial in which all the coefficients and exponents are integers: ...
1
vote
1answer
179 views

Functions that operate on symbolic matrices?

I'd like to write functions that operate on symbolic matrices, and do nothing when fed anything else. ...
3
votes
1answer
214 views

How do you pattern match a DataDistribution

I have a function, f[dist_, samp_]:=somework[dist, samp] that I want to return Null or zero if passed a null distribution. I ...
2
votes
3answers
119 views

Applying several patterns to `Split`

Please consider the following: Split[data, patterns &] patterns=Not[#=="a"]&&Not[#=="b"]&&...&&Not[#=="blabla"]; How can I define ...
7
votes
1answer
236 views

How does Mathematica wrap code for front-end needs? Why does this wrapping affect the evaluation?

Mathematica wraps any expression with some boxing code before showing the evaluation result in the front-end. Unfortunately, the wrapping algorithm and its position in the Mathematica end-to-end flow ...
8
votes
2answers
161 views

Replacing product expressions - named vs. unnamed pattern?

Suppose I have an expression of the form a b c d + x y z The FullForm of this is ...
4
votes
1answer
242 views

Pattern matching in subscripted variables

I am trying to use subscripted variables as symbols and provide assumptions elegantly for them, e.g. in order to simplify logs, I'd like to have ...
2
votes
1answer
118 views

replacement rule to pull independent expression outside of Integrate

I'm trying to write a fairly general replacement rule that will pull expressions independent of the variable of integration outside of Integrate, since Simplify and ...
0
votes
2answers
183 views

Pattern constraint for two or more variables

Is it possible to have a pattern constraint for a function with two or more variables where the pattern is a relation between the vars being accepted e.g. ...
8
votes
3answers
494 views

How can I convert x^2 to x*x?

When I try the following code: a b^2 c /. b c -> e Mathematica gives me: a b^2 c but what I want is: ...
9
votes
4answers
452 views

Using Position (which requires a pattern) in the same manner as Select (which requires a criterion)

I am using Mathematica7. I have a list of lists (creatively named list in the following sample code) containing data. I would like to find the positions of the ...
10
votes
4answers
272 views

How to match expressions with a repeating pattern

The expression I want to match obey a simple pattern that repeats it self a number of times. f[a]@f[b]@f[c]@...@f[X] How would you match all expressions of this ...
5
votes
1answer
325 views

Count sublists which match pattern

I have a list which looks like this: data={{12,0},{0,0},{20,1},{0,0}, {0,-1}}. Now I would like to count the number of sublists which: have both slots zero the ...
7
votes
2answers
206 views

Why does the name of a pattern affect the result of a transformation rule?

I was playing a little dirty, trying to get a template for defining a Curl[] operator. I wrote the following rule, which I knew was going to spit out a few ...
16
votes
1answer
302 views

Is pure pattern matching without PatternTest and Condition Turing-complete?

Note that this question is not a duplicate of that one. It is specifically about the pattern-matching engine, and explicitly excluding those patterns which call back into the full evaluation (i.e. ...
16
votes
2answers
688 views

How do I perform string matching and replacements?

What are, and how do I use Mathematica's string matching and replacement tools?
7
votes
2answers
536 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 ...
7
votes
3answers
437 views

Specifying string patterns in DeleteCases

It seems that DeleteCases is not compatible with string patterns, at least directly (see, for example, this question). Is this true? If so, why is this the case? ...
10
votes
4answers
353 views

How to use pattern matching to assign values to Subscript[f,x_]?

I want to define two subscripted functions Subscript[f,1] and Subscript[f,2]. To keep the assignments local, I would like to ...
1
vote
2answers
148 views

Using patterns in ReplaceAll to extract elements from tuples at arbitrary depths

Please consider the following: I need to extract from MyList all last parts of each 3-tuple. ...
11
votes
4answers
396 views

Assessing argument type in set delayed function definitions

I'm wondering how to properly assess the type of arguments passed to functions defined with :=. I want my functions to be the most efficient, unambiguous and clear ...
12
votes
4answers
280 views

The gap between MapAt and ReplacePart for 2D data tables with headers

Consider a relational table derived from survey data, where each column ("001-01" ...) represents a responder and each row (...
4
votes
1answer
279 views

Path queries for tree-structured data

Can anyone suggest documentation or tutorials for developing path queries and indices for (XML-like) tree-structured data? Suppose data is organized hierarchically in key->value pairs, eg: ...
5
votes
2answers
187 views

Delete contexts from a string representation of a symbol

I want to delete the string representing the context of a symbol. For info I need such a functionality in my ShowIt function defined here I'd like to know how I ...
5
votes
3answers
382 views

position of sequence of elements in list [duplicate]

Possible Duplicate: Finding a subsequence in a list Question The position of {3, 5} is the list {1, 3, 4, 3, 5, 5, 1} is 3. How can such a position ...
39
votes
4answers
2k views

Using a PatternTest versus a Condition for pattern matching

My last question to the site resulted in several answers that involve using pattern matching in Mathematica, a feature I wasn't very familiar with at the time. I am currently reading Mathematica ...
7
votes
1answer
174 views

Built in way to de-list singletons?

Is there a built in method to de-list singleton expressions, like this rule-based solution: expr_ :> If[Length[expr] == 1, First@expr, expr] In data ...
8
votes
3answers
326 views

Find subexpression to minimize leafcount after replacment with temporary variable

Given an expression expr, is there an automated way to find a subexpression subexpr such that replacing ...
25
votes
0answers
473 views

How is pattern specificity decided?

Mathematica has a notion of pattern specificity, which is a partial ordering on patterns. The rules (e.g. DownValues, ...
7
votes
2answers
290 views

Building a tree

Given a list of word characters, such as this one, I'd like to build a tree, similar to this makeTree function, but with the tree in a different format. So, for an input such as ...
13
votes
2answers
336 views

How can I separate a separable function

I have a separable function $f[x,y]$, and I would like to find two functions $g[x]$ and $h[y]$ with $f[x,y]=g[x] h[y]$ where $g[x]$ doesn't depend on $y$ and $h[y]$ doesn't depend on $x$. Ideally, ...
15
votes
2answers
370 views

Successful match in Replace but not in Cases?

I have a little example that exhibits a successful pattern match in ReplaceAll that Cases misses and I wonder if the assembled ...
4
votes
4answers
427 views

Creating lists from a string, separating words from numbers

Say I have a string that contains numbers and words, such as this one: string = "there are 1234 words and numbers 5678 in here $999"; How would I separate the ...
9
votes
1answer
284 views

Selectively clear DownValues

How can I clear a subset of a symbol's DownValues ? For example, suppose I have created some DownValues for $f$ like this: ...