Apply a function to a specific column for every row in a dataframe in R

Question

我想将用户定义的函数应用于R中数据框中每一行的特定列，并将结果保存回列中。

Answer 1

After nearly 3 hours of reading Stack Overflow answers about slightly different use cases and playing around with apply, lapply, sapply etc. here's the code that allows you to do this:

your_function <- function(x) {
    if(x == 3) {
        x = 333
    } else {
        x = 1
    }
}

df$colname <- sapply(df$colname, your_function)