elastic – Elasticsearch for R

August 2, 2017
By

(This article was first published on rOpenSci Blog, and kindly contributed to R-bloggers)

elastic is an R client for Elasticsearch

elastic has been around since 2013, with the first commit in November, 2013.

sidebar – 'elastic' was picked as a package named before the company now known as Elastic
changed their name to Elastic.

What is Elasticsearch?

If you aren't familiar with Elasticsearch, it is a distributed, RESTful search and analytics engine.
It's similar to Solr. It falls in the NoSQL bin of databases, holding data in JSON documents, instead
of rows and columns. Elasticsearch has a concept of index, similar to a database in SQL-land.
You can hold many documents of similar type within a single index. There is powerful search
capabilities, including lots of different types of queries that can be done separately
or combined. And best of all it's super fast.

Other clients

The Elastic company maintains some official clients, including the Python client
elasticsearch-py, and it's higher
level DSL client elasticsearch-dsl.

I won't talk much about it, but we have slowly been working on an R equivalent of the
Python DSL client, called elasticdsl, for
a human friendly way to compose Elasticsearch queries.

Vignettes

Check out the elastic introduction vignette
and the search vignette to get started.

Noteable features

  • elastic has nearly complete coverage of the Elasticsearch HTTP API. If there's
    anything missing you need in this client, let us know! Check out the
    features label
    for features we plan to add to the package.
  • We fail well. This is important to us. We allow the user to choose simple errors
    to just give e.g., 404 HTTP error, or complex errors, including full stack trace
    from Elasticsearch in addition to the HTTP errror. We strive to fail well when
    users give the wrong type of input, etc. as well. Let us know if elastic is not
    failing well!
  • We strive to allow R centric ways of interacting with Elasticsearch. For example,
    in the function docs_bulk, our interface to the Elasticsearch bulk API
    we make it easy to create documents in your Elasticsearch instance from R lists,
    data.frame's and from bulk format files on disk.
  • elastic works with most versions of Elasticsearch. We run the test suite on 11
    versions of Elasticsearch, from v1.0.0 up to v5.5.0. We strive to fail well
    with useful messages when there is a feature no longer available or one that is
    a new feature and not available in previous Elasticsearch versions.
  • Search inputs are flexible: lists and JSON strings both work.
  • Arguably, a noteable feature is that this client has been around nearly 4 years,
    so we've surfaced and squashed many bugs.

Getting help

Setup

Install elastic

install.packages("elastic")

Or get the development version:

devtools::install_github("ropensci/elastic")
library(elastic)

I'm running Elasticsearch version:

ping()$version$number
#> [1] "5.4.0"

Examples

Initialize a client

Using connect()

elastic::connect()
#> transport:  http
#> host:       127.0.0.1
#> port:       9200
#> path:       NULL
#> username:   NULL
#> password:   
#> errors:     simple
#> headers (names):  NULL

By default, you connect to localhost and port 9200. There's paramaters
for setting transport schema, username, password, and base search path (e.g.,
_search or something else).

See bottom of post about possible changes in connections.

Get some data

Elasticsearch has a bulk load API to load data in fast. The format is pretty weird
though. It's sort of JSON, but would pass no JSON linter. I include a few data
sets in elastic so it's easy to get up and running, and so when you run examples
in this package they'll actually run the same way (hopefully).

Public Library of Science (PLOS) data

A dataset inluded in the elastic package is metadata for PLOS scholarly articles.
Get the file path, then load:

plosdat <- system.file("examples", "plos_data.json", package = "elastic")
invisible(docs_bulk(plosdat))

The main search function is Search(). Running it without any inputs searches
across all indices – in this case only the plos index.

Search()
#> $took
#> [1] 1
#>
#> $timed_out
#> [1] FALSE
#>
#> $`_shards`
#> $`_shards`$total
#> [1] 5
#>
#> $`_shards`$successful
#> [1] 5
#>
#> $`_shards`$failed
#> [1] 0
...

Search just the plos index and only return 1 result

Search(index = "plos", size = 1)$hits$hits
#> [[1]]
#> [[1]]$`_index`
#> [1] "plos"
#>
#> [[1]]$`_type`
#> [1] "article"
#>
#> [[1]]$`_id`
#> [1] "0"
#>
#> [[1]]$`_score`
#> [1] 1
#>
#> [[1]]$`_source`
#> [[1]]$`_source`$id
#> [1] "10.1371/journal.pone.0007737"
#>
#> [[1]]$`_source`$title
#> [1] "Phospholipase C-β4 Is Essential for the Progression of the Normal Sleep Sequence and Ultradian Body Temperature Rhythms in Mice"

Search the plos index, and the article document type, sort by title, and query for antibody, limit to 1 result.

First, with Elasticsearch v5 and greater, we need to set fielddata = true if we want to search on or sort on a text field.

mapping_create("plos", "article", update_all_types = TRUE, body = '{
   "properties": {
     "title": {
     "type":     "text",
     "fielddata": true
   }
 }
}')
#> $acknowledged
#> [1] TRUE
Search(index = "plos", type = "article", sort = "title", q = "antibody", size = 1)$hits$hits
#> [[1]]
#> [[1]]$`_index`
#> [1] "plos"
#>
#> [[1]]$`_type`
#> [1] "article"
#>
#> [[1]]$`_id`
#> [1] "568"
#>
#> [[1]]$`_score`
#> NULL
#>
#> [[1]]$`_source`
#> [[1]]$`_source`$id
#> [1] "10.1371/journal.pone.0085002"
#>
#> [[1]]$`_source`$title
#> [1] "Evaluation of 131I-Anti-Angiotensin II Type 1 Receptor Monoclonal Antibody as a Reporter for Hepatocellular Carcinoma"
#>
#>
#> [[1]]$sort
#> [[1]]$sort[[1]]
#> [1] "1"

Get documents

Get document with id=1

docs_get(index = 'plos', type = 'article', id = 1)
#> $`_index`
#> [1] "plos"
#>
#> $`_type`
#> [1] "article"
#>
#> $`_id`
#> [1] "1"
#>
#> $`_version`
#> [1] 1
#>
#> $found
#> [1] TRUE
#>
#> $`_source`
#> $`_source`$id
#> [1] "10.1371/journal.pone.0098602"
#>
#> $`_source`$title
#> [1] "Population Genetic Structure of a Sandstone Specialist and a Generalist Heath Species at Two Levels of Sandstone Patchiness across the Strait of Gibraltar"

Get certain fields

docs_get(index = 'plos', type = 'article', id = 1, fields = 'id')
#> $`_index`
#> [1] "plos"
#>
#> $`_type`
#> [1] "article"
#>
#> $`_id`
#> [1] "1"
#>
#> $`_version`
#> [1] 1
#>
#> $found
#> [1] TRUE

Raw JSON data

You can optionally get back raw JSON from many functions by setting parameter raw=TRUE.

For example, get raw JSON, then parse with jsonlite

(out <- docs_mget(index = "plos", type = "article", id = 5:6, raw = TRUE))
#> [1] "{\"docs\":[{\"_index\":\"plos\",\"_type\":\"article\",\"_id\":\"5\",\"_version\":1,\"found\":true,\"_source\":{\"id\":\"10.1371/journal.pone.0085123\",\"title\":\"MiR-21 Is under Control of STAT5 but Is Dispensable for Mammary Development and Lactation\"}},{\"_index\":\"plos\",\"_type\":\"article\",\"_id\":\"6\",\"_version\":1,\"found\":true,\"_source\":{\"id\":\"10.1371/journal.pone.0098600\",\"title\":\"Correction: Designing Mixed Species Tree Plantations for the Tropics: Balancing Ecological Attributes of Species with Landholder Preferences in the Philippines\"}}]}"
#> attr(,"class")
#> [1] "elastic_mget"
jsonlite::fromJSON(out)
#> $docs
#>   _index   _type _id _version found                   _source.id
#> 1   plos article   5        1  TRUE 10.1371/journal.pone.0085123
#> 2   plos article   6        1  TRUE 10.1371/journal.pone.0098600
#>                                                                                                                                                     _source.title
#> 1                                                                       MiR-21 Is under Control of STAT5 but Is Dispensable for Mammary Development and Lactation
#> 2 Correction: Designing Mixed Species Tree Plantations for the Tropics: Balancing Ecological Attributes of Species with Landholder Preferences in the Philippines

Here, we'll use another dataset that comes with the package on Shakespeare plays.

gbifdat <- system.file("examples", "gbif_data.json", package = "elastic")
invisible(docs_bulk(gbifdat))

Define an aggregation query:

aggs <- '{
    "aggs": {
        "latbuckets" : {
           "histogram" : {
               "field" : "decimalLatitude",
               "interval" : 5
           }
        }
    }
}'

Search the gbif index

res <- Search(index = "gbif", body = aggs, size = 0)$aggregations$latbuckets$buckets
do.call("rbind.data.frame", res)
#>    key doc_count
#> 2  -35         1
#> 22 -30         0
#> 3  -25         0
#> 4  -20         0
#> 5  -15         0
#> 6  -10         0
#> 7   -5         1
#> 8    0         0
#> 9    5         0
#> 10  10         0
#> 11  15         0
#> 12  20         0
#> 13  25         4
#> 14  30         2
#> 15  35         3
#> 16  40         2
#> 17  45        66
#> 18  50       183
#> 19  55       487
#> 20  60       130
#> 21  65        20

Scrolling search – instead of paging

When you want all the documents, your best bet is likely to be scrolling search.

Here's an example. First, use Search(), setting a value for the scroll parameter.

res1 <- Search(index = 'shakespeare', scroll = "1m")

You get a scroll ID back when setting the scroll parameter

res1$`_scroll_id`
#> [1] "DnF1ZXJ5VGhlbkZldGNoBQAAAAAAAAElFnZ2X3FJVWEyUU1HQjl2cFpWUFl0cXcAAAAAAAABJBZ2dl9xSVVhMlFNR0I5dnBaVlBZdHF3AAAAAAAAAScWdnZfcUlVYTJRTUdCOXZwWlZQWXRxdwAAAAAAAAEmFnZ2X3FJVWEyUU1HQjl2cFpWUFl0cXcAAAAAAAABIxZ2dl9xSVVhMlFNR0I5dnBaVlBZdHF3"

Use a while loop to get all results

out1 <- list()
hits <- 1
while (hits != 0) {
  tmp1 <- scroll(scroll_id = res1$`_scroll_id`)
  hits <- length(tmp1$hits$hits)
  if (hits > 0) {
   out1 <- c(out1, tmp1$hits$hits)
  }
}

Woohoo! Collected all 1 documents in very little time.

Now, get _source from each document:

docs <- lapply(out1, "[[", "_source")
length(docs)
#> [1] 4988
vapply(docs[1:10], "[[", "", "text_entry")
#>  [1] "Without much shame retold or spoken of."
#>  [2] "For more uneven and unwelcome news"
#>  [3] "And shape of likelihood, the news was told;"
#>  [4] "Mordake the Earl of Fife, and eldest son"
#>  [5] "It is a conquest for a prince to boast of."
#>  [6] "Amongst a grove, the very straightest plant;"
#>  [7] "That some night-tripping fairy had exchanged"
#>  [8] "Then would I have his Harry, and he mine."
#>  [9] "This is his uncles teaching; this is Worcester,"
#> [10] "Malevolent to you in all aspects;"

Bulk documents

You've already seen the bulk docs API in action above. Above though, we were
using docs_bulk.character – where the input is a character string that's a
file path.

Here, I'll describe briefly how you can insert any data.frame as documents in your
Elasticsearch instance. We'll use the diamonds dataset from the ~54K row ggplot2
package.

#> $acknowledged
#> [1] TRUE
library(ggplot2)
invisible(docs_bulk(diamonds, "diam"))
#> |==================================| 100%
Search("diam")$hits$total
#> [1] 47375

That's pretty easy! This function is used a lot, particularly with data.frame's – so
we get many questions/feedback on this so it will just keep getting better/faster.

TO DO

Connections

We're planning to roll out changes in how you connect to Elasticsearch from elastic.
Right now, you can only connect to one Elasticsearch instance per R session –
your details are set and then recalled internally in each function. We plan to change
this to instantiate a client and then you either call functions on the client
(e.g., using R6) or pass the client object onto functions.

Checkout issue #87 to follow
progress or discuss.

Move to using crul for http

crul is a relatively new R http client – and has async baked in – as well as mocking.
Development should be easier with it as I can mock requests for test suites, and
allow users to toggle async more easily.

Call to action

We can use your help! Elasticsearch development moves pretty fast – we'd love this client to
work with every single Elasticsearch version to the extent possible – and we'd love to
squash every bug and solve every feature request fast.

If you need to use Elasticsearch from R, please try out elastic!

  • Report bugs!
  • File feature requests!
  • Send PR's!

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