CODEWITHSUNDEEP
rdata.table
Juancentro
Juancentro

Reputation: 1117

Function for querying a data.table

I have a data.table called prices that has 3 columns: ticker, date and price. I have run

setkey(prices,ticker,date)

If I do this from the code, it works

prices[list("MSFT",as.Date("2013-01-15")]

returning only the row for MSFT in 2013-01-15 However, if I write this function

getPrice <- function(ticker,date) {
  prices[list(ticker,date)]
}

it returns the whole data.table I suspect that it has something to do with scoping in the i parameter, but I can't get it to work. How do I query the data.table if I don't know the parameters in advance?

Upvotes: 1

Views: 158

Answers (1)

eddi
eddi

Reputation: 49448

Your problem is the variable names in your function. Change them to be e.g. x and y (so that they are not the same as column names in your data.table) and everything will work. What you're doing now is constructing a data.table with all of ticker and date columns and then joining that, thus recovering the original data.

Another (more robust) option is to do smth like this in your function:

getPrice <- function(ticker,date) {
  tmp = list(ticker, date)
  prices[tmp]
}

See FAQs 2.12 and 2.13 for more on this - http://datatable.r-forge.r-project.org/datatable-faq.pdf

Upvotes: 3

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