#r-faq

How-to: dropping factor levels in a subsetted data frame in R #fix #it #programming

dropping factor levels in a subsetted data frame in R

I have a data frame containing a factor. When I create a subset of this data frame using subset() or another indexing function, a new data frame is created. However, the factor variable retains all of its original levels even when they do not exist in the new data frame.

This creates headaches when doing faceted plotting or using functions…

Resolved: How to search for "R" materials? #dev #it #computers

How to search for "R" materials?

“The Google” is very helpful… unless your language is called “R,” in which case it spits out tons of irrelevant stuff.

Anyone have any search engine tricks for “R”? There are some specialized websites, like those below, but how can you tell Google you mean “R” the language? If I’m searching for something specific, I’ll use an R-specific term, like “cbind.” Are…

Fixed Quickly reading very large tables as dataframes in R #dev #it #asnwer

Quickly reading very large tables as dataframes in R

I have very large tables (30 million rows) that I would like to load as a dataframes in R. read.table()has a lot of convenient features, but it seems like there is a lot of logic in the implementation that would slow things down. In my case, I am assuming I know the types of the columns ahead of time, the table does not contain any column…

How to: In R, what is the difference between the and [] notations for accessing the elements of a list?

In R, what is the difference between the [] and [[]] notations for accessing the elements of a list?

R provides two different methods for accessing the elements of a list or data.frame- the [] and [[]] operators.

What is the difference between the two? In what situations should I use one over the other?

Answer: In R, what is the difference between the [] and [[]] notations for accessing the…

How to: How to save a plot as image on the disk?

How to save a plot as image on the disk?

I plot a simple linear regression using R. I would like to save that image as PNG or JPEG, is it possible to do it automatically? (via code)

There are two different questions: First, I am already looking at the plot on my monitor and I would like to save it as is. Second, I have not yet generated the plot, but I would like to directly save it to disk when…

How to: How to unload a package without restarting R?

How to unload a package without restarting R?

I’d like to unload a package without having to restart R (mostly because restarting R as I try out different, conflicting packages is getting frustrating, but conceivably this could be used in a program to use one function and then anotheralthough namespace referencing is probably a better idea for that use).

?librarydoesn’t show any options that…

Fixed How to join data frames in R (inner, outer, left, right)? #dev #it #asnwer

How to join data frames in R (inner, outer, left, right)?

Given two data frames

df1 = data.frame(CustomerId=c(1:6),Product=c(rep("Toaster",3),rep("Radio",3))) df2 = data.frame(CustomerId=c(2,4,6),State=c(rep("Alabama",2),rep("Ohio",1))) > df1 CustomerId Product 1 Toaster 2 Toaster 3 Toaster 4 Radio 5 Radio 6 Radio > df2 CustomerId State 2 Alabama 4 Alabama 6 Ohio

How can I do database style,…

Fixed R Grouping functions: sapply vs. lapply vs. apply. vs. tapply vs. by vs. aggregate #dev #it #asnwer

R Grouping functions: sapply vs. lapply vs. apply. vs. tapply vs. by vs. aggregate

Whenever I want to do something “map”py in R, I usually try to use a function in the apply family. (Side question: I still haven’t learned plyr or reshape would plyr or reshape replace all of these entirely?)

However, I’ve never quite understood the differences between them [how {sapply, lapply, etc.} apply the…