How do you change multiple column names in a Julia (version 0.3) DataFrame?

You might find the names! function more concise:

julia> using DataFrames

julia> df = DataFrame(x1 = 1:2, x2 = 2:3, x3 = 3:4)
2x3 DataFrame
|-------|----|----|----|
| Row # | x1 | x2 | x3 |
| 1     | 1  | 2  | 3  |
| 2     | 2  | 3  | 4  |

julia> names!(df, [symbol("col$i") for i in 1:3])
Index([:col2=>2,:col1=>1,:col3=>3],[:col1,:col2,:col3])

julia> df
2x3 DataFrame
|-------|------|------|------|
| Row # | col1 | col2 | col3 |
| 1     | 1    | 2    | 3    |
| 2     | 2    | 3    | 4    |

One way to do this is with the rename! function. The method of the rename function takes a DataFrame as input though only allows you to change a single column name at a time (as of the development version 0.3 branch on 1/4/2014). Looking into the code of Index.jl in the DataFrames repository lead me to this solution which works for me:

rename!(y.colindex, [(symbol("x$i")=>symbol("col$i")) for i in 1:20])

y.colindex returns the index for the dataframe y, and the next argument creates a dictionary mapping the old column symbols to the new column symbols. I imagine that by the time someone else needs this, there will be a nicer way to do this, but I just spent a few hours figuring this out in the development version 0.3 of Julia, so I thought i would share!