score:2

Accepted answer
var result = _client.getrecords().result
                .selectmany(x => x.category)
                .groupby(x => x)
                .select(x => $"{x.key}-{x.count()}");

score:2

(await _client.getrecords()).selectmany(b => blog.category, (b, c) => new { blog = blog, cat = c })

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