# Tagged Questions

27 views

### Held keys in associations

Jacob Akkerboom commented: Note that PositionIndex does work correctly with held expressions, whereas this is a bit painful to implement using ...
56 views

### Pattern matching to head with HoldFirst

I want to define a function that only operates on expressions with a head from a given list, such as f[expr:(_And|_Or)] := Print["LHS is ", expr[[1]]]; This of ...
173 views

### Why does Plot[Hold[x], {x,0,1}] work?

It appears that, counter to my expectation, all of these (and probably many others) seem to work fine: ...
137 views

### Stopping a head from evaluating more than once

While attempting to answer my own question, Is there a way to "hold" prefix / infix / postfix notation?, I came across the need to evaluate a recursive function only one level deep. For ...
276 views

### Replacing parts of a held expression with held parts of another expression

I'm applying the Trott-Strzebonski technique in order to replace inside a held expression. ...
57 views

### How to extract a variable names (not values) from a list of transformation rules?

I am trying to extract variable names from a list of transformation rules mapping = {var1 -> 'val1', var2 -> 'val2' }. Variables ...
212 views

### Pass unevaluated function with evaluated arguments

I am almost sure that this question has been asked somewhere. I found similar ones, but I cannot find exactly what I need, which might mean that I am on the wrong track. I search a method to pass an ...
133 views

### Converting expression into string without evaluating it

How can one convert a Mathematica expression into a string without the expression being evaluated first? I tried using Hold, but it returns ...
63 views

### Confused with HoldForm in Postfix notation

Why does the following code produce different result? In my mental model, they should be the same. ...
269 views

### Replace symbols with values without evaluation

If I have assigned values to a, b and c: ...
92 views

### Why is held expression evaluated?

Context: I'm studying non-linear dynamics. As part of a bigger problem, I'd like to generate lists of the form {{deq, ic1}, {deq, ic2}, ...}, where ...
161 views

### Creating a custom context with a Hold construct

I'm trying to create a function "InContext" to execute a piece of code inside a certain context (and to return the result of evaluating that piece of code). One approach is to place the code inside a ...
105 views

### Evaluation of second argument to NIntegrate

Apologies if this is a duplicate, but I couldn't find it. The expression Integrate[x^2, Flatten[{{x},{1,2}}]] evaluates properly, to $\frac{7}{3}$. However, ...
135 views

### Passing a joined list of symbols for Module or Block to treat as its own local symbols

The Question I'd like to write a function which itself takes a list of symbols, e.g. Foo[{x, y, z}] to pass to Module ...
208 views

### Why is this expression being held, and how can I evaluate it?

I can't figure out why an expression isn't evaluating, even though there's no Hold* in its FullForm: ...
196 views

### How to join held Lists?

Let's say I have a = Hold@{2+2} b = Hold@{4+4} How can I get Hold@{2+2,4+4} ie join the two held lists ? More ...
114 views

### How to evaluate only arguments, but leave topmost expression unevaluated? [duplicate]

I want to represent expressions mostly in unevaluated form, but being able to evaluate it's subparts. For example, how to evaluate only arguments, but leave topmost expression unevaluated? For ...
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207 views

### Applying a function with the HoldAll attribute inside NestList

I'm trying to write an update function, which can be applied to a list and then to NestList it. As the function has to manipulate the given variable I figured I ...
135 views

### direct assignment to the element in a Table

I have already asked a related question here why set values in this way doesn't work? But I think I have to write the question which I encountered explicitly? ...
269 views

### Make Mathematica wait before replacing?

How can I force Mathematica to completely evaluate a subexpression before using a replacement rule? For example, consider the following definition (for the series of ...