# Tagged Questions

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

81 views

### Evaluation speed of apparently equivalent functions

Consider the following expressions: f[x_Integer] := x, f[x_] := x /; x ∈ Integers, f[x_?IntegerQ] := x All of the expressions above (and probably others which ...
68 views

### Generate all 3-permutations of the set {x, y, z, w, u, t} excluding the ones where 'u' is after 't' [closed]

I have to generate all 3-permutations of a the set $(x, y, z, w, u, t)$ without the ones where the element $u$ is after element $t$. So far I have generated all the the 3-permutations like such <...
100 views

### Applying ReplaceAll to I (imaginary unit) [closed]

Why does I/.I->-I return -I but Exp[-I]/.I->-I yields ...
108 views

### Get the sum with cases

I have the following list: list = {{1, 2}, {2}, {3, 4, 1}, {5, 4}, {3, 3}, {a, b, c}, {e, f}, {g}, {}, {Sin[a], Cos[b]}}; I should use ...
109 views

### Write a function, write a pattern [closed]

I have the following list: list = {{1, 2, 4}, 6, 7, 8, {8, 2}, {3, 4}, {4, 5}, {1, 2, 3, 1}}; (a) I should write a predicate-function in combination with an ...
51 views

### Find/Write a pattern [closed]

I should find a pattern for the following expression: expr = {a^2, a^b, x^4, (x - 1)^2}; And that should be the result: ...
96 views

### Surprising behavior when OptionsPattern is part of a larger pattern

Say we have a pattern defined as: pattern = {foo[OptionsPattern[]] ...}; We can then use MatchQ to see whether an expression ...
94 views

### Removing solutions which are particular cases of others

I have an algorithm which gives me a list of solutions (in matrix form, if it is of any importance) of an equation. Some of these solutions are particular cases of other. For example, in this list ...
125 views

### Dealing Repeated pattern in StringReplace

A problem about StringReplace When I'm running into this problem possible [bug] ...
182 views

### How to trim the zeros from the right of a list? [duplicate]

I need to remove the zeros from the right of an integer list up to the first non-zero element. Such as {0,1,0,0,2,0,0}->{0,1,0,0,2}. Padding zeros can be simply ...
119 views

### Why the flat f[x] is treated as ghostHead_[f[x]]?

While reading this answer I feel confused. If we do not care any specific detail of the original question, then ybeltukov's answer essentially makes use of the following fact ...
1k views

### Finding the period of an array of integers

A simple array of integers is given. The problem is to detect if a pattern is repeatedly occurring in the array, and find the length of that pattern. For example, for ...
93 views

### Can we say that “all functions in Mathematica are some kind of pattern-matching-and-replacement procedures”? [duplicate]

Currently I am studying Mathematica programming, and when I study pattern matching and replacement, I find it is quite similar to functions. So can we say "all functions in Mathematica are some kind ...
307 views

### Empty Blank regression in v10.1

Bug introduced in 10.1 and fixed in 10.2.0 In v10.1.0.0 on Linux, when Blank[] is used in Alternatives with pattern that can ...
160 views

### Express block matrix in terms of matrix basis

I'm trying to construct a function that returns the multiplication table of a matrix Lie algebra. Assuming a basis of matrices, my definitions: ...
219 views

### Assumptions with patterns

I want that Mathematica assumes every symbol like Subscript[s,i] to be evaluate as a real and positive number. I have tried ...
213 views

### How to highlight the elements in a list that match a pattern?

For example, {{1,2,3},{1,2,3,1,2,3,4,5}}with pattern {1,_,3}is transformed to ...
123 views

### Is there a way to search for Arithmetic Progressions in a list?

If you have a list of integers is there a way of searching that list to see if there is a trend of Ax+B in the list? Not using all of the numbers, just seeing what trends like that are embedded in a ...
335 views

### Matching pair of numbers {a,-a}, where a is numeric

Imagine you have a list of pairs of numbers, such as {{2,-2}, {1,5}, {1,-3},{-3,3}} The task is to reduce the given list to a list of pairs of type ...
114 views

### Error when combining Except, “*” and an additional character

Bug introduced in 5 or earlier and persists through 10.4.1 Anyone knows why ...
149 views

### DeleteDuplicates in a list of 2-tuples under condition

Having a list of 2-tuples, I would like to delete such 2-tuples that have 0 at second position, but only those, whose first element is not unique in the list. E.g. ...
140 views

### How do I use ReplaceAll to replace strings of a specified form?

Why is "Xabcde" /. "X" ~~ e__ -> e "Xabcde" and not "abcde"
50 views

### Matching x,y,z,2

I have a list of integers; I would like to replace anything of the form $x,y,z,2$ in such a list with $x+1, y+1, 0, 0$. The problem is that the $2$ may appear at the front, or in the first three ...
195 views

### Better output for NonlinearModelFit “ParameterTable”

The Standard table fo parameters of NonlinearModelFit is obtained from NonlinearModelFit[{{0, 1}, {1, 2}, {3, 3}}, a + b*x, {a, b}, x] %["ParameterTable"]] I ...
332 views

### Why can I not replace a Dataset using a rule?

Simple replacement of a Dataset object does not seem to follow the expected behavior... Dataset[{}] /. _Dataset->1 Returns the empty Dataset not 1 as I would ...
53 views

### Selecting from a list [duplicate]

OK, I know this must be a simple problem, but right now I'm just stuck and need some advice with this :). I have the following list: ...
74 views

### ReplaceRepeated made a single replacement where I expected multiple replacements to be made

This seems like a very simple action: {a, b, c, d, e, f} //. {r___, x_, y___} :> {r, 1, y} but it replaces only the first element giving ...
475 views

I have a list of strings and I would check if there is an empty string element, that's "", because I need to replace it with a "0". I try the following ...
45 views

### FirstPosition returning an error message together with the correct answer

I have the following code: ...
41 views

### How do I match all the subscripted terms in Times?

Suppose I have an expression: $W = A_{i,p,q...}\,\, a_ia_ja_ka_l...$, where $A_{i,p,q...}$ is an expression that does not depend on $a$, the indexes $i,j,k,l,p,q...$ are integers and all the integers ...
92 views

### How to make Simplify/Expand work in patterns?

I am trying to calculate deriv of a complicated function and store the values for reuse. But the FullSimplify in my definition doesn't seem work all the time: ...
180 views

### Extracting numerical coefficients from an expression

I have very large expression and I want to extract and sum up all the numerical coefficients which multiply the summands. For example, expr = x + 2*y + 3*z*w ...
190 views

### Change matrix elements at specific locations?

Let's say I have an array a={{1,2,3}, {4,5,6}, {7,8,9}} I want to have all elements along the diagonal multiplied by 2. ...
163 views

### Can a pattern examine all partitions of a sequence?

Say I have a list: {a, b, c, d}. I'd like to check that the list has some partition, say {{a, b, c}, {d}} such that all the elements of the partition satisfy a ...
144 views

### Replace elements that match pattern

I am using pattern matching to identify elements in a list to be replaced. How can I supply a list of patterns to match and replace all elements in the list that match the pattern? The problem I have ...
100 views

### Removing characters from non-strings

I have a large list of lists that contains mixed data, some real, some strings. The lists are of various lengths and depths. Some of the real data values have an asterisk appended to them, e.g.: <...
522 views

### Determine if all the zeros in a list occur at the end

I have a collection of (short) lists of nonnegative integers. For each, I would like a predicate that decides if all of the zeros in the list appear at the end. For example, ...
114 views

### Compare tree structures in mathematica

Since Mathematica expression is basically a tree structure, I would like to perform tree structure comparison with certain restrictions, for instance that the identity of nodes on the same level be ...
131 views

### Pattern matching with Complex. Feature or a bug?

fixed in 10.1 (windows) I have run into some strange behavior while doing some pattern matching. First, this works as expected: ...
77 views

### How to create a general expression for an integer derivative?

I need MMa to return a general expression for the jth derivative wrt v of v^n. This didn't work: ...
83 views

### How to use pattern matching for integral identities?

I have an unknown pdf f[x], and I need to express integrals involving f[x] as expansions of the moments of f[x]. For example: ...
280 views

### How can I construct a recursive pattern guard?

I am modelling binary trees in Wolfram Language by writing them as three-element lists, like so: binTree = {nodeVal, leftChild, rightChild}. It does not yet matter ...
186 views

### Isolating cross terms

I have a set of expressions that contains terms like $\frac{1}{(x + a + b)(c+d)}$. I would like to simplify the denominator so that products of $a,b,c,d$ are dropped, but $x c$ and $x d$ are kept. ...
75 views

### FilterRules with pattern for name [duplicate]

I have a list of rules and I want to filter it using a pattern for the initial string representing the name of the rule. So that in the example below it filters linearBool even if it is called "linear"...
122 views

### Odd behavior matching powers of pi

I have a long list of generated values from which I want to remove "weird" ones like Sin[Sin[1]] and Pi^2/4. However, trying to ...
132 views

### Output function control and manipulation for efficient computation [closed]

I have taken note of a similar post related to modifying function parameters. I tried to adapt Kuba's solution to this post but I can't get it to work. I will illustrate my problem using a similar ...