Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
2
votes
1answer
89 views
18
votes
1answer
212 views
replacement rules from a pattern and a matching expression
(This seems to be a very basic necessity in a language having pattern-matching capabilities such as Mathematica, yet I struggled for many hours to find a common solution to this problem.)
Suppose ...
3
votes
2answers
77 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
209 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
136 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
208 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
297 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:
...
7
votes
2answers
316 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
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
95 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
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:
...
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.
...
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 ...
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 ...
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
183 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 ...
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
92 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:
...
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 ...
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:
...
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 ...
26
votes
6answers
894 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 ...
9
votes
5answers
674 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 ...
8
votes
2answers
235 views
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 ...
16
votes
1answer
262 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. ...
14
votes
2answers
335 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
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 ...
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? ...
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
287 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 (...
4
votes
1answer
250 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
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 ...
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 ...
30
votes
4answers
786 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
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
298 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
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
...
12
votes
2answers
236 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, ...
