Everyone a great god, and now I encountered such a problem, use the a2 & lt; - the as. The data frame (lapply (a, a.s. Numeric)) characters in the data frame type of data into numerical data, but the more strange is the code above will only character data type forced into NA values, but it looks like data could not be run, but do you have any solution: the character type data into numeric data and does not produce NA values?