Hi there!
I´m using KIRC database from TCGA and downloaded FPKM values, then converted to TPM with this formulas:

FPKMtoTPM <- function(x) {
  return(exp(log(x) - log(sum(x)) + log(1e6)))
}

df <- data %>%
  mutate_if(is.numeric, FPKMtoTPM)

Now i want to convert TPM to log2(TPM+1). How can i do this?

Thanks! 
David
Just as you defined the first function FPKMtoTPM you can define another one for the log transformation of the TPM values

    logTPM <- function(x) {return(log2(x+1))}

    df %>% mutate_if(is.numeric, logTPM)

