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

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12
votes
4answers
354 views

How to enumerate all possible binary associations?

Suppose I have a list of symbols like: {a,b,c,d} I would like to enumerate all possible binary associations (combining symbols and/or sublists pairwise): ...
12
votes
4answers
522 views

Calling Table with custom iterator

I often find myself in situations where I, for example, need to build a table for some expression, but want to set the number of points rather then the step size, so the code ends up looking like this ...
12
votes
4answers
336 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 (...
12
votes
2answers
346 views

Split a Unicode string maintaining uppercase characters

I want to split a string according to a predefined set of substrings (lowercase), though the actual text can contain uppercase characters anyplace. The task is to find the matches, longer preferred ...
12
votes
6answers
305 views

How can I mix the behaviors of StringReplace and ReplaceAll in a single rule?

I'm trying to take a list of the form { {"65 + 3 months", 75}, {"65 + 4 months", 75.1} }, and transform the string part to a number such as 65.25 or 65.333, ...
11
votes
4answers
496 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 ...
11
votes
2answers
427 views

Soft-Match String Comparison

I have a list of names in which I would like to check for duplicates. However, within the list, the duplicates may not show up as exact duplicates of each other - for instance, ...
11
votes
3answers
543 views

Delete duplicates in a list, depending on the sequence of numbers

Below, list is a representative sample of my list, which contains lists of integers. I would like to be able to input: ...
11
votes
1answer
276 views

I can't use PatternSequence with Cases

I have a list of integers: s = {4, 5, 5, 6, 2, 5, 3, 2, 4, 2, 1, 1, 4, 3, 4, 3, 1, 6, 3, 4}; And if I do this, both occurrences of 4 after 3 are replaced. ...
11
votes
2answers
353 views

Should I use \\\“ or \” to match " in regex?

Both of the following return True: ...
10
votes
3answers
830 views

Passing down arguments

In R, one can use ... to pass arguments down to another function. For example ...
10
votes
4answers
316 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 ...
10
votes
3answers
490 views
10
votes
4answers
231 views

Is it possible to separately call the default value of a variable which isn't at the end of the sequence?

After reading this post I recalled an old question I once met. We know that we can set default values for variables of a function: ...
10
votes
4answers
357 views

What is the correct way to use specific rule for specific pattern match when parsing an expression?

update: Thanks for the answers below. But I noticed they do not handle the following special cases: lis=1 and lis=z , ...
10
votes
4answers
440 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 ...
10
votes
3answers
188 views

Pattern matching on Orderless functions inside Hold

MatchQ[Hold[1 + 2], Hold[2 + 1]] returns False. But in the presence of a Blank[] in the ...
10
votes
4answers
409 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 ...
10
votes
1answer
644 views

Mathematica equivalent of regex '\w{2,3}'

It beats me to write the Mathematica pattern equivalent to the regex: \w{2,3} Any ideas?
10
votes
4answers
243 views

Recognizing special cases of a defined function for permuted arguments

I have a number of ugly ways to implement the following pattern recognition task, but I'm looking for something elegant to keep my notebook tidy. I need to define a function of six variables ...
10
votes
1answer
151 views

Why doesn't repeated PatternSequence work with explicit pattern names?

Why would this work: Clear[f] f[a : PatternSequence[b_, c_]] := {a}; f[1, 2] (* {1, 2} *) and this also works: ...
10
votes
1answer
341 views

Mixing patterns with string patterns

I have imported an XML document into Mathematica. It is now represented as Symbolic XML expression in the variable xml: ...
9
votes
5answers
327 views

How can I remove matching sublists from my list?

I want to use DeleteCases (or any appropriate function) to remove elements of a list, which in turn are lists of fixed size. The rule I wish to apply is that any ...
9
votes
3answers
267 views

Splitting a list in which figures vary from negative to positive

Consider the following list: data={4078, 256, -1266, -388, 1290, 1368, 1446, 1524, 2}; I would like to split any kind of such list always, when figures turn form ...
9
votes
4answers
619 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 ...
9
votes
5answers
369 views

Repeating Digits

I have written ...
9
votes
2answers
809 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 ...
9
votes
2answers
255 views

Why doesn't Cases match all instances of XMLElement, given Infinity levelspec?

Why doesn't Cases match all instances of XMLElement, given Infinity levelspec? ...
9
votes
1answer
101 views

Apply N only outside a certain function

1 + f[1] // N gives 1. + f[1.] I don't want the argument of f evaluated by N; I ...
9
votes
1answer
110 views

Why can't I remove the {0, 0} in Circle[{0, 0}] using pattern matching?

Why does Circle[{0, 0}] /. List[_?NumericQ ..] :> Sequence[] return Circle[{0, 0}] yet ...
9
votes
3answers
488 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 ...
9
votes
1answer
315 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: ...
9
votes
3answers
725 views

Pattern matching a pattern with patterns

Confusing title, I know. But the question is, if we have two patterns which have the same general structure but different names used in the patterns and different names: ...
9
votes
1answer
229 views

How to define function that can change patterns

Given time series data as follows: data = {{{2011, 1, 13}, 10}, {{2011, 2, 14}, 17}, {{2011, 3, 15}, 20}, {{2012, 1, 16}, 30}, {{2012, 2, 17}, 40}}; ...
8
votes
8answers
868 views

How can a power of 0 or 1 be replaced?

Consider this given example for ReplaceAll 1 + x^2 + x^4 /. x^p_ -> f[p] This returns ...
8
votes
3answers
196 views

Select and Blank

I try to filter sublists of a list which match a pattern. test = {{"String1", "a"}, {"String2", "b"}, {"String3", "a"}, {"String4", "a"}}; The result should ...
8
votes
4answers
274 views

Check in a series if there exists adjacent values with less than a certain number of missing values

I'm working with a large number of series of different experiments, where there exist a lot of experiments where there are no entries. I now want to draw a sample where there should exist at least ...
8
votes
3answers
498 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: ...
8
votes
3answers
571 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? ...
8
votes
1answer
178 views

How to tell when a job is too big for the pattern matcher?

Pattern matching is great but it has its limitations. Consider sorting a list of numbers from smallest to largest: ...
8
votes
1answer
116 views

CSS Selectors for Symbolic XML

Symbolic XML is a convenient way of managing XML in Mathematica, at least for casual use or small tasks. Here and elsewhere you can find examples of XML handling in Mathematica, including XSLT/XPath ...
8
votes
2answers
201 views

Orderless pattern matching of rule lists

I am looking for a compact way to specify a pattern to match a rule list with MatchQ that allows for enumerating the rules in the rule list in an arbitrary order. ...
8
votes
3answers
322 views

Patternmatching sets

How to match set-patterns against sets? A set (in the mathematical sense) is a list of elements without repetition and order of elements does not matter. For example, we have a pattern set ...
8
votes
2answers
196 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 ...
8
votes
2answers
110 views

Unexpected result from StringReplace

The following works as expected. StringReplace["xxxyxz", "x" ~~ _ -> "ww"] "wwwwww" And so does this. ...
8
votes
4answers
431 views

Best way to modify values in a list of rules?

Recently I had to solve a problem similar to this: Let's say I have a list of list of rules ...
8
votes
1answer
273 views

Does Mathematica use first order or second order order unification?

When Mathematica is pattern-matching expressions, does it use first order or second order unification. Just to clarify the difference between first order and second order unification: In Second order ...
8
votes
1answer
203 views

MatchQ and patterns for similar lists

I can't seem to find the right set of patterns to independently match two different lists. Simplified versions of the lists are as follows: ...
8
votes
2answers
700 views

Mathematica rule substitution memory

First I present the specific programming question, and then I provide further background details. Given an expression in Mathematica, say f=3x+7y, there are two ...
8
votes
1answer
102 views

How to get a list of all expressions in a notebook matching a certain pattern?

Suppose I have a Mathematica notebook saved to a certain location on disk. Given a pattern I need to get the list of all expressions matching this pattern that appear in input, output or print cells ...