CSV.read: why do String columns show up as PooledArrays?

New to Julia
3

Here’s the onehot-encoder function I wrote. It’s now failing by saying the return value “onehot” is not defined.

function onehotenc(df::DataFrame)

    # Loop to develop onehot-encoding
    for col in eachcol(df)
        
        # Can we determine if the column is a String and only encode it if it is?
        if col isa String
            
            # How long is the current column we're going to onehot-encode?
            len = length(col)

            # Save the unique values (or Set) and how many there are for our initial zeros matrix
            vals = unique(col)

            # Set up the Dict key-value pairs to save the Boolean operation results
            # For each val in vals make that val a key (:key) with 
            # and fill that column with Boolean falses to begin with
            dict = Dict(Symbol(val) => falses(len) for val in vals)

            # Once the Dict is populated convert it to a DataFrame
            onehot = DataFrame(dict)

            # Change the value from 0 to 1 in the zero DataFrame based on whether the unique value matches the original DF
            for (i, v) in enumerate(col)
                # At the row and col of the current enumerated col value, set the value to true
                # EX: In the onehot DF at row 1, column :A set equal to true
                # EX: In the onehot DF at row 2, column :B set equal to true
                onehot[i, Symbol(v)] = true
            end
        end
    end
    
    return onehot
    
end