How do I write a function in r to do cacluations on a record?

Question

In C# I am used to the concept of a data set and a current record. It would be easy for me to write a complicated calc-price function with conditions on the current record.

Answer 1

For my own notes on Gregor's answer

IsPrettyIf <-function(row){
 ret ="N"  
 if(row$Petal.Width > 0.3) { ret="Y"}
 return(ret)
}

 
df <- iris
df$PrettyLoop ="" # add a column and initialize all the cells to be empty
for(i in 1:5) {
  df$PrettyLoop[i] = IsPrettyIf(df[i,])
  cat("Row",i, "is Pretty?",df$PrettyLoop[i],"\n")
}

The bit that trips me up is that row$PrettyLoop is like a cell and df$PrettyLoop is like a column, thinking with the spreadsheet analogy.