Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
13
votes
3answers
299 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 ...
7
votes
1answer
111 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
72 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:
...
3
votes
1answer
109 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
96 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 ...
1
vote
1answer
123 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.
...
4
votes
2answers
148 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:
...
3
votes
1answer
165 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
98 views
Applying several patterns to `Split`
Please consider the following:
Split[data, patterns &]
patterns=Not[#=="a"]&&Not[#=="b"]&&...&&Not[#=="blabla"];
How can I define ...
8
votes
2answers
113 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
...
12
votes
2answers
187 views
Pattern that matches colors
Suppose I'm writing a function that takes a color as a parameter; for example:
drawShape[color_] := Graphics[{Style[Disk[], color]}];
But if the caller inputs an ...
7
votes
1answer
213 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 ...
4
votes
1answer
150 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
...
0
votes
0answers
93 views
How to collect terms of a given type (with subscript and power) in an expression?
Suppose that I have an expression:
...
1
vote
1answer
51 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
156 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.
...
1
vote
0answers
53 views
Evaluation in mapping constructs [closed]
I'm trying to use ReplacePart inside of Map, where the address of the element being replaced is the domain of the map, like this:
...
8
votes
3answers
476 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:
...
7
votes
1answer
160 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 ...
4
votes
4answers
186 views
How to pick out the element in a list of lists which satisfies a particular condition?
I have got a list:
...
18
votes
4answers
429 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
4answers
202 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 ...
8
votes
2answers
236 views
26
votes
6answers
900 views
Find zero crossing in a list
I'm looking for a function that finds the index of the zero-crossing points of a list. Before I go making my own subroutine to do this, I was wondering if anyone knows of any built-in Mathematica ...
0
votes
1answer
161 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
189 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 ...
7
votes
2answers
229 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
5answers
675 views
Counting negative values in list
I would like to count the negative values of a list.
My approach was Count[data, -_] which doesn't work.
How can I tell Mathematica to count all numbers with ...
10
votes
4answers
249 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
118 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
289 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
234 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 (...
5
votes
2answers
166 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 ...
6
votes
3answers
273 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? ...
4
votes
3answers
171 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 ...
7
votes
1answer
147 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 ...
5
votes
3answers
182 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 ...
21
votes
0answers
299 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, ...
12
votes
2answers
238 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, ...
7
votes
2answers
225 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
...
9
votes
1answer
153 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:
...
4
votes
4answers
288 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 ...
11
votes
3answers
237 views
Returning an unevaluated expression with values substituted in
Let's say I have a function
formula[x_List] := (x[[1]] - x[[2]]) + (x[[3]] - x[[4]]);
and I want to pass it a variable and get back the unevaluated formula with ...
3
votes
1answer
103 views
Pattern matching a multivariate derivative
I can extract the parameters of a single variable derivative with the rule
D[f[x], x] /. Derivative[order_][fcn_][variable_] ->
{order, fcn, variable}
...
3
votes
2answers
165 views
Highlighting text with StringReplacePart but also using Style, Subscript
For a Natural Language Processing analysis task it's desirable to highlight a text string programmatically according to XML tags that reference specific words or phrases.
The XML tags specify the ...
8
votes
1answer
153 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
4answers
283 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 ...
5
votes
2answers
149 views
Pattern matching deletion of list items [duplicate]
Possible Duplicate:
How can I remove B -> A from a list if A -> B is in the list?
I'm working toward building a graph and use some code to construct my rules which results in a form ...
6
votes
2answers
212 views
Rule for orderless function Times
I have problems extending a replacement rule.
Schematically, this is the situation:
I have an expression and a rule, and they work perfectly together.
...
11
votes
2answers
173 views
