# Tagged Questions

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

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### Is there an elegant way of delaying evaluation of A==B when calling a function that uses this pattern

Suppose I wanted to define a number of functions that accepts expressions of the form: ...
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### Making a replacement on the numerator and denominator of a rational number

It's isn't a big deal, but when I run the following I don't get the output I expect. After discussing this in the comments it appears it has to do with being an atomic expression. ...
55 views

### Avoiding misconversion of data with ToExpression function [closed]

I've got a list of data with the following structure which can be easily converted To expresion by some manipulation such as ...
338 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, ...
694 views

### How to detect loops in a vector field?

Given a vector field and I'd like to detect if there are streamlines in closed patterns. For example, if the input is a vector field like this: ...
239 views

### Pattern and Orderless function

I'm a Mathematica beginner. I am exploring the use of patterns and (only for fun) am trying to implement a permutations function. My (dirty) code is: ...
65 views

### Substituting a list of values into a function [closed]

g[p_] := Mod[19^(-1 + p), p^2] This is my function, and the set of values I have is the first 999 prime numbers. I made a table listing the first 999 prime ...
212 views

### ReplaceAll problem

Bug introduced in 10.1 and persisting through 10.2 or later Confirmed, as bug, by WRI: [CASE:3402234] I am trying to combine terms of the type ...
228 views

### Strange behavior with Cases and Position with SetDelayed

I feel like I must be missing something simple and obvious here, but this has me scratching my head. This works as expected: ...
77 views

### Patterns with inactive integrals

I am trying to do algebra on unsolved integrals but not getting the pattern-matching right. I want the correlation of f[x] and f[x]+a*d[x], normalized by their self correlations. ...
131 views

### Matching Symbol or Subscript, but not Symbol arguments of Subscript

I'm trying to get a list of all the variables in a symbolic expression. Some are named with Symbols, some are named with ...
236 views

### Cases vs Select, Pattern vs Pure function [duplicate]

What is the difference between having Cases with selection condition presented by pattern and a with pure function as condition? ...
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### How to compare and remove x-coordinates (and the associated y-coordinates) that are less than previous x-coordinates?

I am using Mathematica version 9.0 and am trying to compare and remove x-coordinates, and the associated y-coordinate, that are less than previous x-coordinates. Below is an example using sample data. ...
310 views

### Mma10 mystery: Failure of pure function substitution with Interpretation?

Bug introduced in 10.0.0 and fixed in 10.0.1 I had code to display with subscripts from Displaying index as subscript on output: e.g. C[i] -> C_i with Notation[...] or Interpretation[..]? which ...
147 views

### Select largest number using pattern

I have the following expression: myExpr=R[C[2],B].(II+R[C[3],C[2]].(II+R[C[4],C[3]])) I need to create a pattern which would replace the ...
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### How to pick max/mins of elements that match patterns?

I have a list of complicated expressions that involve indexed coefficients. For example: expr={m[5],c[3]*m[1]^2+m[2],Sqrt[m[2]+3*m[3]*c[8],foo[m[3]*m[5]]}; How ...
264 views

### Replace matrix rows conditionally while avoiding For loop

I have the following variables: myMatrix={{0,0,0},{0,0,0},{0,0,0},{0,0,0},{0,0,0},{0,0,0}} myIndices={1,3} I need to replace the rows ...
72 views

### Confusion over blank sequence in pattern matching

My overall goal was to produce a list of heads used in a graphics output. For an example I used: ...
159 views

### Find position avoiding For loop

I have a list: {a,b,c,d,e,f} And a function sizeFunc[element_] which returns the size ...
256 views

### Help with PatternSequence

I have a list of strings of the form list = {str1, str2, strx, str3, .., str10} each string contains both letters and numbers, except for ...
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### Dropping rational coefficients

I have a list of expressions (they all are exact numeric quantities, not containing any variables), some of them have integer or rationals coefficients, or complex coefficients with rational or ...
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### How can I name patterns in a Switch expression?

Suppose I have an expression and want to match it against successive patterns and return an expression corresponding to the first pattern that matched. In that case, I can use ...
78 views

### Trouble simplifying using Replace

I have the following expression: w.a.b.r+w.c.d.r I want to get: w.(a.b+c.d).r So far I used ReplaceRepeated: ...
163 views

### An equivalent to Condition that I can use anonymously when string pattern matching

When I name a pattern I'm working with, that name stands for the same particular expression wherever it shows up. That's a basic precept of how the Wolfram Language's pattern-matching works. But if I ...
182 views

### Match a variable name pattern [duplicate]

I have a list of variables: {RBI,RCD,ASD,FGH} I want to select only those whose name starts with R. Using the pattern Rx_ ...
299 views

### How to identify all rules that match pattern type? [duplicate]

I would like to be extend the below solution to be able to find get all rules from the list step[2] that match the generic pattern k_Digit_p. Where k and p are not ...
60 views

### How to use EvenQ[] in patterns? [duplicate]

This works: (w[1] + w[2] + w[3]) /. w[s_] -> If[s == 2, w[s], 0] (* w[2] *) This doesn't: ...
149 views

### How to Negate a Pattern Test and Transform a List of Strings to a JSON array

First I would like to find out how to negate a pattern and based on this I would like to solve this little problem on how to transform a list of strings to a JSON array. This is how I started working ...
106 views

### Delete Element within a List based on the Order [closed]

I want to do the following, deleting the element of a list that do not match an increasing order as example: {1,2,3,4,6,5,7,8}->{1,2,3,4,6,7,8} I've thought of using DeleteCases but I'm not able to ...
819 views

### How to inject an evaluated expression into a held expression? [duplicate]

I know that there are methods to structurally manipulate held expressions (discussed e.g. here), but I failed to apply those for this particular problem: ...
407 views

### Opposite of Alternatives

I was looking at this question (here) and I tried to find any thing gives the opposite of Alternatives. In other words, some pattern matching function that gives ...