How can I concatenate (merge, combine) two values? For example I have: tmp = cbind(“GAD”, “AB”) tmp # [,1] [,2] # [1,] “GAD” “AB” My goal is to concatenate the two values in “tmp” to one string: tmp_new = “GAD,AB” Which function can do this for me? 12 Answers 12
I have a data frame with two columns. First column contains categories such as “First”, “Second”, “Third”, and the second column has numbers that represent the number of times I saw the specific groups from “Category”. For example: Category Frequency First 10 First 15 First 5 Second 2 Third 14 Third 20 Second 3 I … Read more
I want to write trycatch code to deal with error in downloading from the web. url <- c( “http://stat.ethz.ch/R-manual/R-devel/library/base/html/connections.html”, “http://en.wikipedia.org/wiki/Xz”) y <- mapply(readLines, con=url) These two statements run successfully. Below, I create a non-exist web address: url <- c(“xxxxx”, “http://en.wikipedia.org/wiki/Xz”) url[1] does not exist. How does one write a trycatch loop (function) so that: When … Read more
I have a vector of numbers: numbers <- c(4,23,4,23,5,43,54,56,657,67,67,435, 453,435,324,34,456,56,567,65,34,435) How can I have R count the number of times a value x appears in the vector? 20 Answers 20 You can just use table(): > a <- table(numbers) > a numbers 4 5 23 34 43 54 56 65 67 324 435 453 456 … Read more
In R, mean() and median() are standard functions which do what you’d expect. mode() tells you the internal storage mode of the object, not the value that occurs the most in its argument. But is there is a standard library function that implements the statistical mode for a vector (or list)? 35 Answers 35
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 … Read more
I’m trying to initialize a data.frame without any rows. Basically, I want to specify the data types for each column and name them, but not have any rows created as a result. The best I’ve been able to do so far is something like: df <- data.frame(Date=as.Date(“01/01/2000″, format=”%m/%d/%Y”), File=””, User=””, stringsAsFactors=FALSE) df <- df[-1,] Which … Read more
I have a data frame containing a factor. When I create a subset of this dataframe using subset or another indexing function, a new data frame is created. However, the factor variable retains all of its original levels, even when/if they do not exist in the new dataframe. This causes problems when doing faceted plotting … Read more
How to check if a vector contains a given value? 7 s 7
R provides two different methods for accessing the elements of a list or data.frame: [] and [[]]. What is the difference between the two, and when should I use one over the other? 12 s 12