PooledVectors for isbitstypes of small size? #982
Description
data = """a b c d
A BB CCC DDDD
A BB CCC DDDD
""" |> IOBuffer
df = CSV.File(data; header = 1) |> DataFrame
df[!, :a] # 2-element PooledVector{String1, UInt32, Vector{UInt32}}
df[!, :b] # 2-element PooledVector{String3, UInt32, Vector{UInt32}}
df[!, :c] # 2-element PooledVector{String3, UInt32, Vector{UInt32}}
df[!, :d] # 2-element PooledVector{String7, UInt32, Vector{UInt32}}