formattable in R shows data type name in header

Question

I'm printing a dataframe in R, using "formattable". I'm executing it in a Jupyter notebook with an R kernel. Here the code:

df = data.frame(
     Return = percent(accumulReturn[selcol,1]),
     AnnualizedReturn = percent(annualizedReturn[selcol,1]/100),
     MonthlyReturn = percent(annualizedReturn[selcol,2]/100),
     Vola = percent(volatilityTable[selcol,1]),
     Sharpe = round(annualizedReturn[selcol,1] / 100 / volatilityTable[selcol,1],2),
     Drawdown = percent(dds)
 )

t <- formattable(df)
t

In the headers of the columns it shows the data type of each column, which is very distracting. I don't want to see the data type there. How can I do it?

I tried using different formatters, but they seem to get ignored by the function call.