get.sid.list:
Get PubChem Substance ID's Associated With A Compound and Vice Versa
Description
Each unique compound is associated with a number of substances. Given
a CID it is possible to determine the associated substance ID's. Conversely
given a SID it is useful to identify all CIDs that are associated with it
Depending on whether the input was a CID or SID, the return value is a numeric vector of
SID's or a single numeric CID, respectively.
Details
Even though PUG REST allows one to specify multiple input ID's these methods operate on
single identifiers, allowing the user to parallelize multiple queries. In addition, this
approach allows the package to cache results for individual input identifiers