将“ *”移动到R中的新列

Question

Hello I have a column in a data.frame, it has many rows, eg,

df = data.frame("Species" = c("*Briza minor", "*Briza minor", "Wattle"))

I want to make a new column "Species_new" where the "*" is moved to the end of the character string, eg,

df = data.frame("Species" = c("*Briza minor", "*Briza minor", "Wattle"),
            "Species_new" = c("Briza minor*", "Briza minor*", "Wattle"))

Is there a way to do this using gsub? The manual example would take far too long as I have approximately 50,000 rows.

Thanks in advance

Answer 1

One option is to capture the * as a group and in the replacement reverse the backreferences

df$Species_new <- sub("^([*])(.*)$", "\\2\\1", df$Species)
df$Species_new
#[1] "Briza minor*" "Briza minor*" "Wattle"    

NOTE: * is a metacharacter meaning 0 or more, so we can either escape ( \\\\* ) or place it in brackets ( [] ) to evaluate the raw character ie literal evaluation

Answer 2

Thanks so much for the quick response, I also found a workaround;

df$Species_new = sub("[*]","",df$Species, perl=TRUE)

differences = setdiff(df$Species,df$Species_new)

tochange = subset(df,df$Species == differences)
toleave = subset(df,!df$Species == differences)

tochange$Species_new = paste(tochange$Species_new, "*", sep = "")

df = rbind(tochange,toleave)