R - Use literal string parameters in R functions

Question

How do I reference parameters that are literal strings ?

In the example below I want to get the min CONTACT_DATE in the dataframe

fx1  <- function(df1, pDate ) { 
  cat( as.Date( df1[ pDate] ) %>% min( na.rm = TRUE) );
}

# Print the Min CONTACT_DATE 
fx1 ( df_Del0 , "CONTACT_DATE");

Thanks for your help Aubrey

tried different ways like

cat ( as.Date(df1[eval(parse(pDate)]) %>% min( na.rm = TRUE);

akrun · Accepted Answer · 2021-07-01 17:48:57Z

1

Use the [[ instead of [ to extract as a vector as as.Date or min works on vectors

fx1 <- function(df1, pDate) {
        min(as.Date(df1[[pDate]]), na.rm = TRUE)
}

The %>% is a magrittr chain. Chaining can be done in base R with |> (from R 4.1.0)

fx1 <- function(df1, pDate) {
        df1[[pDate]] |>
         as.Date() |>
         min(na.rm = TRUE)
}

Also, cat/print just print the output into console and doesn't have a return value. We can return the output for future use instead of just printing

edited Jul 1, 2021 at 17:48

answered Jul 1, 2021 at 17:22

akrun

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