Exploring the NCBI taxonomy database using Entrez Direct

I’ve been meaning to write about Entrez Direct, henceforth called edirect, for some time. This tweet provided me with an excuse:

OK tweeps, I'm looking for estimates of species richness in insects. Any orders, families, or genera with good estimates you know of? pls RT

— Robert Lanfear (@RobLanfear) April 1, 2015

This post is not strictly the answer to that question. Instead we’ll ask: which parent IDs of records for insects in the NCBI Taxonomy database have the most species IDs?

PubMed Publication Date: what is it, exactly?

File this one under “has troubled me (and others) for some years now, let’s try to resolve it.”

Let’s use the excellent R/rentrez package to search PubMed for articles that were retracted in 2013.

library(rentrez)

es <- entrez_search("pubmed", "\"Retracted Publication\"[PTYP] 2013[PDAT]", usehistory = "y")
es$count
# [1] 117

117 articles. Now let’s fetch the records in XML format.

xml <- entrez_fetch("pubmed", WebEnv = es$WebEnv, query_key = es$QueryKey, 
                    rettype = "xml", retmax = es$count)

Next question: which XML element specifies the “Date of publication” (PDAT)?

When is db=all not db=all? When you use Entrez ELink.

Just a brief technical note.

I figured that for a given compound in PubChem, it would be interesting to know whether that compound had been used in a high-throughput experiment, which you might find in GEO. Very easy using the E-utilities, as implemented in the R package rentrez:

library(rentrez)
links <- entrez_link(dbfrom = "pccompound", db = "gds", id = "62857")
length(links$pccompound_gds)
# [1] 741

Browsing the rentrez documentation, I note that db can take the value “all”. Sounds useful!

links <- entrez_link(dbfrom = "pccompound", db = "all", id = "62857")
length(links$pccompound_gds)
# [1] 0

That’s odd. In fact, this query does not even link pccompound to gds:

length(names(links))
# [1] 39
which(names(links) == "pccompound_gds")
# integer(0)

It’s not a rentrez issue, since the same result occurs using the E-utilities URL.

The good people at ropensci have opened an issue, contacting NCBI for clarification. We’ll keep you posted.

What the world needs is: lists of Entrez database fields

You know the problem. You want to qualify your NCBI/Entrez database search term using a field. For example: “autism[TIAB]”, to search PubMed for the word autism in either Title or Abstract. Problem – you can’t find a list of fields specific to that database.

Now you can. Follow the links in this public Dropbox file, to see a CSV file containing name, full name and description of the fields for each Entrez database.

Code to generate the files is listed below. This may or may not be the first in an occasional, irregular “what the world needs” series.

#!/usr/bin/ruby
require 'rubygems'
require 'bio'
require 'hpricot'
require 'open-uri'

Bio::NCBI.default_email = "me@me.com"
ncbi = Bio::NCBI::REST.new

ncbi.einfo.each do |db|
  puts "Processing #{db}..."
  File.open("#{db}.txt", "w") do |f|
    doc = Hpricot(open("http://eutils.ncbi.nlm.nih.gov/entrez/eutils/einfo.fcgi?db=#{db}"))
    (doc/'//fieldlist/field').each do |field|
      name = (field/'/name').inner_html
      fullname = (field/'/fullname').inner_html
      description = (field/'description').inner_html
      f.write("#{name},#{fullname},#{description}\n")
    end
  end
end

Querying NCBI Entrez database fields using Ruby

Here’s a problem. You’d like to construct a complex query at NCBI Entrez using various fields. Example:

“9606”[Taxonomy ID]

to limit your search to Homo sapiens. Except – you don’t know which fields are available for the database that you want to query.