I wonder if it's correct to say:
"Graphs are a special data structure."
Here, "graphs" are plural, but "a special data structure" is singular. I remember I have seen this type of sentence before, but I cannot give a reference.
I wonder if it's correct to say:
"Graphs are a special data structure."
Here, "graphs" are plural, but "a special data structure" is singular. I remember I have seen this type of sentence before, but I cannot give a reference.
It's grammatical, but it doesn't parse very well.
Consider this:
The problem with the particular sentence in the question is that it's unexpected. Even though the syntax is valid, it's not what we'd expect to hear, because on first glance it appears to confuse a plurality with a singularity (although it actually doesn't). As such, it's slightly unidiomatic.
One variation that sounds better simply inserts two words:
Other variations replace the verb: