为数据帧的“类”提供向量

You know how you can supply a vector of names to a data frame to change the col or row names of a dataframe. Is there a similar method to supply a vector of names that alters the class of each column in a dataframe? You can do this when you read in a dataframe with read.table using colClasses. What about if the dataframe is created inside R?You know how you can supply a vector of names t