# Analytics Component

The Analytics Component allows users to calculate complex statistical aggregations over result sets.

The component enables interacting with data in a variety of ways, both through a diverse set of analytics functions as well as powerful faceting functionality. The standard facets are supported within the analytics component with additions that leverage its analytical capabilities.

## Analytics Configuration

The Analytics component is in a contrib module, therefore it will need to be enabled in the `solrconfig.xml` for each collection where you would like to use it.

Since the Analytics framework is a search component, it must be declared as such and added to the search handler.

For distributed analytics requests over cloud collections, the component uses the `AnalyticsHandler` strictly for inter-shard communication. The Analytics Handler should not be used by users to submit analytics requests.

To use the Analytics Component, the first step is to install this contrib module’s plugins into Solr — see the Solr Plugins section on how to do this. Note: Method with `<lib/>` directive doesn’t work. Instead copy `${solr.install.dir}/dist/solr-analytics-x.x.x.jar` to `${solr.install.dir}/server/solr-webapp/webapp/WEB-INF/lib/`, as described in the lib directories documentation.

Next you need to register the request handler and search component. Add the following lines to `solrconfig.xml`, near the defintions for other request handlers:

For these changes to take effect, restart Solr or reload the core or collection.

## Request Syntax

An Analytics request is passed to Solr with the parameter `analytics` in a request sent to the Search Handler. Since the analytics request is sent inside of a search handler request, it will compute results based on the result set determined by the search handler.

For example, this curl command encodes and POSTs a simple analytics request to the the search handler:

``````curl --data-binary 'analytics={
"expressions" : {
"revenue" : "sum(mult(price,quantity))"
}
}'
http://localhost:8983/solr/sales/select?q=*:*&wt=json&rows=0``````

There are 3 main parts of any analytics request:

Expressions
A list of calculations to perform over the entire result set. Expressions aggregate the search results into a single value to return. This list is entirely independent of the expressions defined in each of the groupings. Find out more about them in the section Expressions.
Functions
One or more Variable Functions to be used throughout the rest of the request. These are essentially lambda functions and can be combined in a number of ways. These functions for the expressions defined in `expressions` as well as `groupings`.
Groupings
The list of Groupings to calculate in addition to the expressions. Groupings hold a set of facets and a list of expressions to compute over those facets. The expressions defined in a grouping are only calculated over the facets defined in that grouping.
 Optional Parameters Either the `expressions` or the `groupings` parameter must be present in the request, or else there will be no analytics to compute. The `functions` parameter is always optional.

## Expressions

Expressions are the way to request pieces of information from the analytics component. These are the statistical expressions that you want computed and returned in your response.

### Constructing an Expression

#### Expression Components

An expression is built using fields, constants, mapping functions and reduction functions. The ways that these can be defined are described below.

Sources
Mapping Functions
Mapping functions map values for each Solr Document or Reduction. The provided mapping functions are detailed in the Analytics Mapping Function Reference.
• Unreduced Mapping: Mapping a Field with another Field or Constant returns a value for every Solr Document. Unreduced mapping functions can take fields, constants as well as other unreduced mapping functions as input.

• Reduced Mapping: Mapping a Reduction Function with another Reduction Function or Constant returns a single value.

Reduction Functions
Functions that reduce the values of sources and/or unreduced mapping functions for every Solr Document to a single value. The provided reduction functions are detailed in the Analytics Reduction Function Reference.

#### Component Ordering

The expression components must be used in the following order to create valid expressions.

1. Reduced Mapping Function
1. Constants
2. Reduction Function
1. Sources
2. Unreduced Mapping Function
1. Sources
2. Unreduced Mapping Function
3. Reduced Mapping Function
2. Reduction Function

This ordering is based on the following rules:

• No reduction function can be an argument of another reduction function. Since all reduction is done together in one step, one reduction function cannot rely on the result of another.

• No fields can be left unreduced, since the analytics component cannot return a list of values for an expression (one for every document). Every expression must be reduced to a single value.

• Mapping functions are not necessary when creating functions, however as many nested mappings as needed can be used.

• Nested mapping functions must be the same type, so either both must be unreduced or both must be reduced. A reduced mapping function cannot take an unreduced mapping function as a parameter and vice versa.

#### Example Construction

With the above definitions and ordering, an example expression can be broken up into its components:

``div(sum(a,fill_missing(b,0)),add(10.5,count(mult(a,c)))))``

As a whole, this is a reduced mapping function. The `div` function is a reduced mapping function since it is a provided mapping function and has reduced arguments.

If we break down the expression further:

• `sum(a,fill_missing(b,0))`: Reduction Function
`sum` is a provided reduction function.

• `a`: Field

• `fill_missing(b,0)`: Unreduced Mapping Function
`fill_missing` is an unreduced mapping function since it is a provided mapping function and has a field argument.

• `b`: Field

• `0`: Constant

• `add(10.5,count(mult(a,c)))`: Reduced Mapping Function
`add` is a reduced mapping function since it is a provided mapping function and has a reduction function argument.

• `10.5`: Constant

• `count(mult(a,c))`: Reduction Function
`count` is a provided reduction function

• `mult(a,c)`: Unreduced Mapping Function
`mult` is an unreduced mapping function since it is a provided mapping function and has two field arguments.

• `a`: Field

• `c`: Field

### Expression Cardinality (Multi-Valued and Single-Valued)

The root of all multi-valued expressions are multi-valued fields. Single-valued expressions can be started with constants or single-valued fields. All single-valued expressions can be treated as multi-valued expressions that contain one value.

Single-valued expressions and multi-valued expressions can be used together in many mapping functions, as well as multi-valued expressions being used alone, and many single-valued expressions being used together. For example:

`add(<single-valued double>, <single-valued double>, …​)`
Returns a single-valued double expression where the value of the values of each expression are added.
`add(<single-valued double>, <multi-valued double>)`
Returns a multi-valued double expression where each value of the second expression is added to the single value of the first expression.
`add(<multi-valued double>, <single-valued double>)`
Acts the same as the above function.
`add(<multi-valued double>)`
Returns a single-valued double expression which is the sum of the multiple values of the parameter expression.

### Types and Implicit Casting

The new analytics component currently supports the types listed in the below table. These types have one-way implicit casting enabled for the following relationships:

TypeImplicitly Casts To
BooleanString
DateLong, String
IntegerLong, Float, Double, String
LongDouble, String
FloatDouble, String
DoubleString
Stringnone

An implicit cast means that if a function requires a certain type of value as a parameter, arguments will be automatically converted to that type if it is possible.

For example, `concat()` only accepts string parameters and since all types can be implicitly cast to strings, any type is accepted as an argument.

This also goes for dynamically typed functions. `fill_missing()` requires two arguments of the same type. However, two types that implicitly cast to the same type can also be used.

For example, `fill_missing(<long>,<float>)` will be cast to `fill_missing(<double>,<double>)` since long cannot be cast to float and float cannot be cast to long implicitly.

There is an ordering to implicit casts, where the more specialized type is ordered ahead of the more general type. Therefore even though both long and float can be implicitly cast to double and string, they will be cast to double. This is because double is a more specialized type than string, which every type can be cast to.

The ordering is the same as their order in the above table.

Cardinality can also be implicitly cast. Single-valued expressions can always be implicitly cast to multi-valued expressions, since all single-valued expressions are multi-valued expressions with one value.

Implicit casting will only occur when an expression will not "compile" without it. If an expression follows all typing rules initially, no implicit casting will occur. Certain functions such as `string()`, `date()`, `round()`, `floor()`, and `ceil()` act as explicit casts, declaring the type that is desired. However `round()`, `floor()` and `cell()` can return either int or long, depending on the argument type.

## Variable Functions

Variable functions are a way to shorten your expressions and make writing analytics queries easier. They are essentially lambda functions defined in a request.

In the above request, instead of writing `mult(price,quantity)` twice, a function `sale()` was defined to abstract this idea. Then that function was used in the multiple expressions.

Suppose that we want to look at the sales of specific categories:

``````{
"functions" : {
"clothing_sale()" : "filter(mult(price,quantity),equal(category,'Clothing'))",
"kitchen_sale()" : "filter(mult(price,quantity),equal(category,\"Kitchen\"))"
},
"expressions" : {
"max_clothing_sale" : "max(clothing_sale())"
, "med_clothing_sale" : "median(clothing_sale())"
, "max_kitchen_sale" : "max(kitchen_sale())"
, "med_kitchen_sale" : "median(kitchen_sale())"
}
}``````

### Arguments

Instead of making a function for each category, it would be much easier to use `category` as an input to the `sale()` function. An example of this functionality is shown below:

Variable Functions can take any number of arguments and use them in the function expression as if they were a field or constant.

### Variable Length Arguments

There are analytics functions that take a variable amount of parameters. Therefore there are use cases where variable functions would need to take a variable amount of parameters.

For example, maybe there are multiple, yet undetermined, number of components to the price of a product. Functions can take a variable length of parameters if the last parameter is followed by `..`

In the above example a variable length argument is used to encapsulate all of the costs to use for a product. There is no definite number of arguments requested for the variable length parameter, therefore the clothing expressions can use 3 and the kitchen expressions can use 2. When the `sale()` function is called, `costs` is expanded to the arguments given.

Therefore in the above request, inside of the `sale` function:

• `add(costs)`

is expanded to both of the following:

• `add(material, tariff, tax)`

• `add(material, construction)`

### For-Each Functions

Although the above functionality allows for an undefined number of arguments to be passed to a function, it does not allow for interacting with those arguments.

Many times we might want to wrap each argument in additional functions. For example maybe we want to be able to look at multiple categories at the same time. So we want to see if `category EQUALS x OR category EQUALS y` and so on.

In order to do this we need to use for-each lambda functions, which transform each value of the variable length parameter. The for-each is started with the `:` character after the variable length parameter.

In this example, `cats:` is the syntax that starts a for-each lambda function over every parameter `cats`, and the `_` character is used to refer to the value of `cats` in each iteration in the for-each. When `sale("Clothing", "Kitchen")` is called, the lambda function `equal(category,_)` is applied to both Clothing and Kitchen inside of the `or()` function.

Using all of these rules, the expression:

```sale("Clothing","Kitchen")```

is expanded to:

```filter(mult(price,quantity),or(equal(category,"Kitchen"),equal(category,"Clothing")))```

by the expression parser.

## Groupings And Facets

Facets, much like in other parts of Solr, allow analytics results to be broken up and grouped by attributes of the data that the expressions are being calculated over.

The currently available facets for use in the analytics component are Value Facets, Pivot Facets, Range Facets and Query Facets. Each facet is required to have a unique name within the grouping it is defined in, and no facet can be defined outside of a grouping.

Groupings allow users to calculate the same grouping of expressions over a set of facets. Groupings must have both `expressions` and `facets` given.

### Facet Sorting

Some Analytics facets allow for complex sorting of their results. The two current sortable facets are Analytic Value Facets and Analytic Pivot Facets.

#### Parameters

`criteria`

The list of criteria to sort the facet by.

It takes the following parameters:

`type`
The type of sort. There are two possible values:
• `expression`: Sort by the value of an expression defined in the same grouping.

• `facetvalue`: Sort by the string-representation of the facet value.

`Direction`
(Optional) The direction to sort.
• `ascending` (Default)

• `descending`

`expression`
When `type = expression`, the name of an expression defined in the same grouping.
`limit`
Limit the number of returned facet values to the top N. (Optional)
`offset`
When a limit is set, skip the top N facet values. (Optional)

### Value Facets

Value Facets are used to group documents by the value of a mapping expression applied to each document. Mapping expressions are expressions that do not include a reduction function.

• `mult(quantity, sum(price, tax))`: breakup documents by the revenue generated

• `fillmissing(state, "N/A")`: breakup documents by state, where N/A is used when the document doesn’t contain a state

Value Facets can be sorted.

#### Parameters

`expression`
The expression to choose a facet bucket for each document.
`sort`
A sort for the results of the pivot.
 Optional Parameters The `sort` parameter is optional.
 Field Facets This is a replacement for Field Facets in the original Analytics Component. Field Facet functionality is maintained in Value Facets by using the name of a field as the expression.

### Analytic Pivot Facets

Pivot Facets are used to group documents by the value of multiple mapping expressions applied to each document.

Pivot Facets work much like layers of Analytic Value Facets. A list of pivots is required, and the order of the list directly impacts the results returned. The first pivot given will be treated like a normal value facet. The second pivot given will be treated like one value facet for each value of the first pivot. Each of these second-level value facets will be limited to the documents in their first-level facet bucket. This continues for however many pivots are provided.

Sorting is enabled on a per-pivot basis. This means that if your top pivot has a sort with `limit:1`, then only that first value of the facet will be drilled down into. Sorting in each pivot is independent of the other pivots.

#### Parameters

`pivots`
The list of pivots to calculate a drill-down facet for. The list is ordered by top-most to bottom-most level.
`name`
The name of the pivot.
`expression`
The expression to choose a facet bucket for each document.
`sort`
A sort for the results of the pivot.
 Optional Parameters The `sort` parameter within the pivot object is optional, and can be given in any, none or all of the provided pivots.

### Analytics Range Facets

Range Facets are used to group documents by the value of a field into a given set of ranges. The inputs for analytics range facets are identical to those used for Solr range facets. Refer to the Range Facet documentation for additional questions regarding use.

#### Parameters

`field`
Field to be faceted over
`start`
The bottom end of the range
`end`
The top end of the range
`gap`
A list of range gaps to generate facet buckets. If the buckets do not add up to fit the `start` to `end` range, then the last `gap` value will repeated as many times as needed to fill any unused range.
`hardend`
Whether to cutoff the last facet bucket range at the `end` value if it spills over. Defaults to `false`.
`include`
The boundaries to include in the facet buckets. Defaults to `lower`.
• `lower` - All gap-based ranges include their lower bound.

• `upper` - All gap-based ranges include their upper bound.

• `edge` - The first and last gap ranges include their edge bounds (lower for the first one, upper for the last one) even if the corresponding upper/lower option is not specified.

• `outer` - The `before` and `after` ranges will be inclusive of their bounds, even if the first or last ranges already include those boundaries.

• `all` - Includes all options: `lower`, `upper`, `edge`, and `outer`

`others`
Additional ranges to include in the facet. Defaults to `none`.
• `before` - All records with field values lower then lower bound of the first range.

• `after` - All records with field values greater then the upper bound of the last range.

• `between` - All records with field values between the lower bound of the first range and the upper bound of the last range.

• `none` - Include facet buckets for none of the above.

• `all` - Include facet buckets for `before`, `after` and `between`.

 Optional Parameters The `hardend`, `include` and `others` parameters are all optional.

### Query Facets

Query Facets are used to group documents by given set of queries.

#### Parameters

`queries`
The list of queries to facet by.