read.csv ;check.names=F; R;Look at the picture,why it works a treat?-CodePudding

Sorry for the code,because I try to type some codes to generate this data.frame like in the picture,but i failed due to the "if".We know that "if" is a reserved word in R(like else,for, while ,function).And here, i deliberately use the "if" as the column name (the 2nd column),and see whether R will generate some novel things. So using another way, I type the "if" in the excel and save as the format of csv in order to use read.csv.

Question is: Why "if." changes to "if"?(After i use check.names=FALSE)

CodePudding user response：

?read.csv describes check.names= in a similar fashion:

check.names: logical.  If 'TRUE' then the names of the variables in the
          data frame are checked to ensure that they are syntactically
          valid variable names.  If necessary they are adjusted (by
          'make.names') so that they are, and also to ensure that there
          are no duplicates.

The default action is to allow you to do something like dat$<column-name>, but unfortunately dat$if will fail with Error: unexpected 'if' in "dat$if", ergo check.names=TRUE changing it to something that the parser will not trip over. Note, though, that dat[["if"]] will work even when dat$if will not.

If you are wondering if check.names=FALSE is ever a bad thing, then imagine this:

dat <- read.csv(text = "a,a\n2,3")
dat
#   a a.1
# 1 2   3

dat <- read.csv(text = "a,a\n2,3", check.names = FALSE)
dat
#   a a
# 1 2 3

In the second case, how does one access the second column by-name? dat$a returns 2 only. However, if you don't want to use $ or [[, and instead can rely on positional indexing for columns, then dat[,colnames(dat) == "a"] does return both of them.