How do you use sapply() with a "list" that includes two columns of data?

I am currently using sapply to call a weighted mean function that takes two inputs, a date and a date frame of multiple values per date,

sapply(unique(sort(d$Date, decreasing=TRUE)), WeightedMean, data=d))

WeightedMean <- function(date, data) {...}

but I would like to update this function to take three inputs. I have created the code below, but am unable to reference both inputs in my WeightedMean function,

sapply(unique(d[order(d$Date, d$Id, decreasing=TRUE), c("Date", "Id")]), 
    WeightedMean, data=d)

WeightedMean <- function(date, id, data) {...}

Note that the WeightedMean function will filter the data by date and id and then calculate a summary value. Is there a way I can update the above code to pass two开发者_如何学C parameters to the function?

You can use mapply instead if sapply. (The m means "multiple arguments".)

ordered_data <- unique(d[order(d$Date, d$Id, decreasing = TRUE), c("Date", "Id")])
with(ordered_data, mapply(WeightedMean, Date, Id))

By using an anonymous function.

You don't provide a working example, so the following code is untested but should work:

sapply(unique(d[order(d$Date, d$Id, decreasing=TRUE), c("Date", "Id")]), 
    function(x){WeightedMean(x$Date, x$Id, data=x)})