Questions tagged [query]

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39
votes
1answer
743 views

Visualizing Type System Operations

With the introduction of Dataset in version 10, Mathematica acquired a static type-checking subsystem. A fair number of dataset-related questions here on MSE ...
24
votes
1answer
616 views

Struggling to understand Query

The documentation for Query starts with: ...
21
votes
2answers
387 views

Query: adding additional operator changes meaning of preceding operators

Consider the following query: Range[5] // Query[Select[EvenQ] /* Append[1], f] (* {f[2], f[4], 1} *) It selects the even numbers, applies ...
17
votes
1answer
283 views

Aggregation queries on lists of associations in 10.3

Bug introduced in 10.3.0 and fixed in 10.3.1 Bug introduced in 10.3.0 and fixed in 10.4.0 First bug, see first part of the question Second bug, see update part Some aggregation queries applied to ...
13
votes
5answers
1k views

Applying a function to a Dataset column conditional on another slot's value

How to apply a function to a column conditional on another slot's value? The Dataset documentation show only how to apply a function to named slots independently. The ...
13
votes
2answers
338 views

Does anyone know a way to use patterns in Query?

This question is a follow up from my previous question. Query has a nice syntax that allows it to apply functions on association based on specific ...
12
votes
2answers
383 views

Query datasets with "variable" named slots

I want to query a Dataset object, e.g. select some entries using ...
12
votes
0answers
175 views

Unix-like reference to parent and root Association?

Is there a syntax or function to reference parent and root when querying nested Associations similar to Unix' ".." and "/", eg "cd ../../mydir". ? Here's a typical application of the root construct....
11
votes
2answers
192 views

A subtlety in Query

Let us consider a simple Dataset: ds=Dataset[{<|"a"->12,"b"->4|>,<|"a"->7,"b"->8|>,<|"b"->3|>}] Column "b" is easy to find: <...
11
votes
2answers
270 views

Simplifying a reverse Fold for a Query

Is there a simpler way to parametrize this tail-recursive expression to be applied as a Query (for processing a nested ...
11
votes
1answer
293 views

10.0.2 breaks a recursive "trie" query

Bug introduced in 10.0.2 and fixed in 10.2 The 10.0.2 Dataset type system complication breaks a recursive trie constructor that worked in 0.1: ...
11
votes
2answers
209 views

Large Dataset query fails if column contains Missing

In version 11.0 (Win 8.1 Pro) a query on a large Dataset for a column that contains Missing fails most unceremoniously. With <...
11
votes
1answer
187 views

Preventing Keys from appearing in Query Output (+ the casting of Ascending/Descending operators)

One of the challenges of coming to grips with Query's on Association's and Datasets is ...
9
votes
2answers
249 views

Slicing an Association with named key span without normalizing?

Is there way to slice an Association with named key span? Span currently doesn't accept named keys: ...
9
votes
2answers
188 views

Getting slices of a nested Association via Query

I'd like to get specific slices from a nested database-like Association through Query. Take for example this toy database of ...
9
votes
3answers
306 views

Problem constructing Association tables with some operators

fixed in 10.0.2 First, set up the example Dataset from the documentation: titanic = ExampleData[{"Dataset", "Titanic"}]; Why ...
9
votes
1answer
154 views

Generating Google BigQuery API Access Token in Wolfram Language

I'm working on a Wolfram Language Package to connect into Google Bigquery (that I'll make public available). In order to finish It, I need to solve a last step, that is how to get an authentication ...
8
votes
2answers
177 views

Query inside Dynamic triggers continuous high CPU load for FE

Here is a (vicious) problem I am able to reproduce with v12 and v11.3 (previous versions not tested) and OSX. This is a minimal example to demonstrate it (even if it seems useless here I do need <...
8
votes
1answer
395 views

Transpose fail in 11.1 Dataset

The type system underlying Dataset seems a total kludge, as soon as one issue is fixed, here it recurs in a slightly different form - and difficult to isolate in minimal examples. Here's a failure ...
8
votes
1answer
85 views

Unexpected behavior of PreIncrement when querying associations

For reasons I won't go into here, I became curious about the what would happen should I make a query that applies PreIncrement to one key in a list of associations....
7
votes
2answers
260 views

How does Query decide the order in which the functions are applied?

First of all I know that Query is a nice way to organize your functions that are applying at specific levels of an expression. But I don't understand the order in ...
7
votes
3answers
311 views

Applying a function by Key pattern, preserving Association order

Any convenient ways to apply a function to Keys that match a pattern in an Association? Method should handle: Mixture of ...
7
votes
1answer
293 views

Possible bug involving Dataset/Query and RightComposition

Bug introduced in 10.0.0 and fixed in 10.0.1 Short Version Why are the results of the following expressions different? ...
6
votes
1answer
309 views

How to filter this nested list of Association

For example, I have the following data ...
6
votes
1answer
379 views

Filtering Query Nested Data (Dataset and Association)

I am trying to filter a nested Dataset. I have some data that looks like this (curated for this example): ...
6
votes
2answers
144 views

Nothing in a Query

In Mathematica 10, Nothing is defined as to automaticaly disappear when used in a list or in an association, and moreover with the property that it returns ...
6
votes
1answer
117 views

Mapping (Query) a function at multiple locations in nested data via All, Span

For this data: dt = <|"a"-> <|"x"-> 1|>,"b"-> <|"y"-> 2|>,"c"-> <|"z"->3|>|> It’s awkward when mapping the same ...
6
votes
1answer
292 views

Select query with named slot lookups?

Given this Dataset fragment (copy-paste friendly version at bottom) Can this query be simplified by referencing named slots directly in the ...
5
votes
1answer
155 views

How can I understand this example of Query taken from current Mathematica documentation?

...
5
votes
2answers
313 views

How to lookup by a string key after GroupBy? Inconsistent data type handling

This is relates to a bug that was introduced in 10.0.0 and fixed in 10.0.1 It also relates to an issue that has yet to be corrected. After applying GroupBy to a ...
5
votes
1answer
88 views

Operator form for Histogram of multiple datasets?

I would like to plot a histogram for multiple datasets in a dataset query, but can't quite seem to make it work in operator notation: ...
5
votes
2answers
545 views

Remove rows from dataset using query

MyDataSet[Select[#point[Fsr] == 1 &]] returns the row I want to delete, now I am trying what looks to me the most logic command to remove these rows, which is <...
5
votes
1answer
333 views

Query Dataset to check if row contains any from a set of values

For a given keyless dataset, I can query to return the rows whose columns contain a specific value. For example: ...
4
votes
2answers
119 views

How to pull out the underlying query syntax being used by dataset?

Consider the following dataset. titanic = ExampleData[{"Dataset", "Titanic"}] If I use the lookup syntax of the dataset like following it creates an equivalent <...
4
votes
1answer
72 views

How can default valued be added in a Query?

I'm not understanding the the default values are not used to produced a length of 0 in the following example. What is the right way to add default values during a query? ...
4
votes
2answers
135 views

Select dataset rows that meet a mathematical criterion in a column

Here is a simple dataset: ...
4
votes
1answer
76 views

A simple way to extract information from this dataset with Query?

I have a dataset comparable to the following (you may wrap it in Dataset if you like). I am looking for a relatively simple way to query it and extract information. ...
4
votes
1answer
181 views

Passing values from a list to Select during a Dataset query

Given a Dataset: ...
4
votes
2answers
34 views

How to Quiet an operator to avoid Query fail

This Query fail, due to divide by zero error message... <|"a" -> 1, "b" -> 0|> // Query[#a/#b &] Missing["Failed"] ...can be prevented by ...
4
votes
1answer
84 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 ...
4
votes
2answers
91 views

Simple dataset query

Why does taking a Part fail in a Dataset query function when there is an operation in the index argument? ...
4
votes
2answers
123 views

Using subquery in Query of Dataset

I want to create a Query to a Dataset that will select a subset of three columns, modify the date column in this subset (to month), group by month and a second column (location), take the group means ...
4
votes
0answers
106 views

How to get parent key in Query on Association/Dataset?

Is there a general and terse method to obtain the parent key of the current "position" in a Query of an Association/...
3
votes
3answers
744 views

Select specific rows of a dataset

I am struggling with extracting specific rows from a dataset. ...
3
votes
1answer
146 views

Query from Association of Associations Dataset

I have a rather large dataset comprised of Association of Associations. For better or worse, I've converted this into a Dataset. Here is a simplified version of ...
3
votes
1answer
84 views

Dataset type system fail with composite keys and Infinity

In 11.1, a Dataset consisting of an Association with composite keys with an Infinity causes failure in keying-in: ...
3
votes
2answers
141 views

Composition with Transpose failure with Dataset

Is the failure of the 2nd Transpose here a known bug? Dataset[{{0, 10}, {2, 11}, {3, 12}}][ Transpose /* Map[MinMax] /* Transpose] // Normal ...
3
votes
0answers
65 views

Aligning input form of a sequence of Queries

Is there a way to modify the parser, or define options, to align the indentation of a sequence of Queries on a Dataset? Given: ds = <|"a" -> 1, "b" -> <|"c" -> 2|>, "d" -> <|"e" -> 3, "f" ...
2
votes
1answer
290 views

Query and Dataset Syntax Peculiarities

Question Can someone please explain to me the syntax of Query and why its behavior is so befuddling to me at the moment? I am going to go through a few simple ...
2
votes
2answers
444 views

Query in Lists Mathematica - Pivot table

Recently, I finished a simulation, and I got the following data: ...