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Questions tagged [associations]

Questions on the associative data-structure introduced in Mathematica version 10.

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7
votes
1answer
74 views

Reversing a GroupBy operation

Suppose that I have a this list of associations ...
6
votes
1answer
87 views

How to use a function as a value in an association? [on hold]

I just started learning Mathematica. I was wondering if it is possible to use a function as an value in an association. Ideally, it would be something like this: ...
2
votes
2answers
51 views

How to associate the elements of a list to numbers?

I am having problems to understand the association function. I have a list of lists containing numbers: ...
8
votes
2answers
166 views

Taking the first element in a list of associations

I have the following list which is built up of associations, that is, ...
5
votes
3answers
71 views

Sort Associations by its Values (which are nested lists)

I have associations where the values are nested lists: ...
14
votes
3answers
268 views

Evaluated vs. unevaluated Association

This question might have a remote connection to my older question, it is also about sameness of expressions and subtle differences observable only in certain forms. I encountered this strange ...
3
votes
1answer
83 views

Edit value in nested Association

Here is a simplified version of my problem. I have a nested Association. ...
5
votes
3answers
288 views

Changing Row Keys into Normal Rows

I have a dataset with column and row keys: ...
6
votes
2answers
122 views

How to define a functional that produces at runtime a function by evaluating selected parts in its definition?

Consider the following functional as an example: ...
3
votes
2answers
67 views

Row Keys in Datasets: JoinAcross row keys; Demoting or deleting row keys

I want to combine two datasets that share row keys but have different column keys. Visually, this looks like a JoinAcross on the row keys to me, but the column of row keys doesn't appear to be named. ...
7
votes
2answers
96 views

Creating a new Dataset column using a map from a second Dataset

Say I have two datasets: one is a detailed list of events, and one is a coarse list of events. I want to add a column to the detailed list from the coarse list (for the purposes of sorting). For ...
11
votes
3answers
306 views

Move the outer key inward in an association

I have a list that looks like: ...
0
votes
0answers
25 views

Having trouble distributing a large association to sub-kernels

The following seems to work based on memory usage. ...
5
votes
3answers
225 views

Iterate over deepest values in a nested Association

Is it possible to iterate over the values of the deepest layer of keys in a nested association? For example: ...
1
vote
0answers
49 views

Wrapping an association with a specialization of the buildin `Set` (=) function?

I want to wrap some association data into a dedicated symbol (S by example) ...
1
vote
2answers
73 views

How to use KeyValuePattern with individual replacement rules?

What's the syntax to use individual replacement rules for key-value patterns? This returns only the first match: ...
4
votes
4answers
133 views

Neat redistribution of association values

Given an original association: original = <| "a" -> {a1, a2}, "b" -> {b1, b2}, "c" -> {c1, c2} |> and a set of redistribution rules e.g. <...
1
vote
2answers
70 views

Create Dataset from lists

Let's assume I created the following dataset: ...
2
votes
1answer
35 views

Hierarchically adding {…keys..}->value to an association

Given a list of keys {"a","b","c"} and a value 3 (associated to the last key) I want to define a function that is equivalent to ...
4
votes
1answer
115 views

Get Windows registry into Mathematica as an association

Windows probably is the only operating system that has a separate database of configuration instructions and paths. The windows registry looks exactly like a giant nested association. Also probably is ...
4
votes
1answer
65 views

Inconsistency in getting Keys, Values and Query for nested Rules

Querying nested Rule expressions of the form a -> v -> b // FullForm Rule[a,Rule[v,b]] for ...
2
votes
1answer
50 views

Turns nested Lists into nested Associations, ReplaceAll for list vs ReplacsAll for association

I want to transform some nested lists into nested associations except the "rows"->List pattern. Here is the example ...
1
vote
1answer
54 views

Sorting each column in a nested list contained in an association

I have an Association which contains three arrays 200x1000x2. Each row m of a matrix denotes a different set of parameters, while each column n contains the outcomes of the function for a specific ...
0
votes
2answers
66 views

Association on a list [closed]

I have a dataset under this form : sentence = {sentence1, sentence2, sentence3,...} and a list of label : label = {1,2,3,4,5,6,7...} both have same length ! So I want to make an association ...
4
votes
1answer
215 views

Inexact numbers as keys in Association?

Can someone explain me how Mathematica's Associations behave with inexact numbers as keys: <| 0.22499999999999964` -> a |> [0.22499999999999965`] and <...
3
votes
1answer
67 views

Reducing boilerplate with associations

I'm looking for advice either on alternative ways to approach my problem in general, or specifically on meta-programming (which seems to me to be a way around this). In my work I have databases of ...
1
vote
0answers
44 views

How do I Select when the key of an association is a multi-word string [closed]

I have imported some survey responses into a Dataset. I now want to select those rows where the response to "participant type" == "Virtual". I discovered that this ...
2
votes
1answer
130 views

Deleting missing values from a dataset

I wanted to create a dataset of all UFO sightings in April of 2018. The AssociationThread doesn't want to work, because some of the entries are missing value, what ...
19
votes
4answers
568 views

Is it possible to avoid unpacking when merging Association?

For example, if we have assoc = AssociationThread[{1, 2, 3} -> RandomReal[1., {3, 10}]]; and ...
7
votes
3answers
231 views

Obtaining a matrix of complex values from associations giving the real and imaginary parts of each element?

I have a list of associations keyed by real and imaginary numbers, like so: ...
2
votes
1answer
56 views

Converting an expression with strings to an association

I have an expression which contains a bunch of strings and some complex valued numeric factors in front. A couple of summands might look like this: ...
4
votes
2answers
164 views

Picking/Selecting in an association

suppose I have 2 associations t1=<|"a" -> 1, "b" -> 2, "c" -> 3, "d" -> 4|> and ...
5
votes
1answer
98 views

Define an access by key ( structure[key] ) for a custom structure struct?

I have some "complicated" data that I want to encapsulate into a "struct": For instance (imagine that data have several fields): ...
7
votes
5answers
330 views

Unexpected behaviour of Nothing inside List inside Association

When evaluating the following input: <|a -> {c, d, e}|> /. d -> Nothing I get (expression 1): ...
3
votes
1answer
43 views

Ranking polynomials based on global maxima

Suppose I have the following polynomials in an association i.e. <|...|>, they are: ...
0
votes
4answers
148 views

Is there a way to order elements in an Association?

...
5
votes
2answers
103 views

How to prevent arguments UpValues from being used in selective functions

Ok, I know the simple answer is to set some form of Hold attribute to the function but bear with me for a bit while I explain my motivation and why that is not quite what I want. I have a collection ...
1
vote
1answer
227 views

Bottom-most left-most entries in a sparse array

I have a list bdrs of SparseArrays, which represent the boundary matrices of a chain complex $R^{d_0}\overset{\partial_1}{\...
4
votes
1answer
161 views

Delete zeros from a sparse array [duplicate]

Why doesn't SparseArray automatically remove zero entries? The code ...
7
votes
0answers
66 views

Substitute for Association inside Compile?

Associations are not compilable, so I’m looking for a workaround to this. That is, I need a mutable hashtable-like data structure with fast key value lookups ...
10
votes
3answers
328 views

Min and Max of a list of Associations

I am trying to find the minimum values for all elements in a list of associations, below is an example ...
3
votes
2answers
256 views

Iterate over keys of association

How do you iterate over the keys or rules of an association (in any order)? E.g. for <|"0"->"a", "1"->"b", "2"->"c"|> I would like to either ...
2
votes
3answers
109 views

Merge Associations and replace absent value with 0

I have two associations like this ...
3
votes
1answer
48 views

KeySelect via Not[StringMatchQ[Pattern]] fails

I have an Association asc that has mixed type Keys: ...
0
votes
1answer
137 views

Aggregate function problem

I use a function to do something similar to a SQL sum. I've asked about simplifying it in another post. I'm still using this function and it works well for aggregates like ...
6
votes
1answer
64 views

unexpected result from augmented assignment to association

Is the last of these results expected? If so, how? ...
10
votes
1answer
104 views

Parallelize[MapIndexed[…,Association[…]]] returns broken result

Bug introduced in 10.0.2 or earlier and persisting through 12.0 Confirmed: CASE:4041910 Consider the following example: ...
5
votes
1answer
233 views

Parallelize the construction of sparse matrices

I'm trying to parallelize a few constructions of chain complexes (given as a list of sparse matrices). I have a function that for any column (or row) computes the list of nonzero entries in that ...
1
vote
0answers
42 views

Extracting Parts of Speech

I am looking to parse the ConstituentsTree from TextStructure. Someone already asked how to get the proper nouns out of a text here: Extract names from a document I am looking for a more general ...
4
votes
2answers
92 views

speedy update of list of associations

Suppose as is a list of associations that I want to update. For example: ...