问题
I've run into the following issue
vec <- c("a11","b21","c31")
df <- data.frame(a = c(0,0,0), b = c(1,1,1), row.names = vec)
df["a",]
returns
df["a",]
a b
a11 0 1
However,
"a" %in% vec
and
"a" %in% rownames(df)
both return False
R is allowing for partial matching of the string when using letter followed by numbers for row names. I have replicated this on R v3.2.2 and R v3.2.1. Even
df[["a",1,exact=T]]
returns 0
Is there anything I can set such that R does not allow this partial matching?
回答1:
Weird, didn't even realize the partial matching was a thing.
Instead of indexing into the dataframe directly, you could try to identify records that exact match on rowname separately and construct an indexing vector from the result, like so:
> ix <- 'a' == row.names(df)
> df[ix,]
<0 rows> (or 0-length row.names)
or equivalently (but more concisely):
> df['a' == row.names(df),]
Alternatively, if you coerce the object to a data.table it will only return exact matches:
> library(data.table)
> dt <- data.table(df)
> dt[,ix := vec]
> setkey(dt, ix)
> dt['a']
a b ix
1: NA NA a
> dt['a11']
a b ix
1: 0 1 a11
回答2:
Why not try:
df[grep(pattern = "a", x = rownames(df)),]
Which would return:
> df[grep(pattern = "a", x = rownames(df)),] a b a11 0 1
Making use of grep would provide you with addittional flexibility, for example if you want to match row names that would have a only:
> df[grep(pattern = "^a$", x = rownames(df)),] [1] a b <0 rows> (or 0-length row.names)
来源：https://stackoverflow.com/questions/34233235/r-returning-partial-matching-of-row-names