如何从数据框中删除特殊字符

Question

I have imported data from a url and converted it to a data frame using the following code:

url <-"http://apims.doe.gov.my/v2/hourly2.php"
tables<- readHTMLTable(url)
try<-do.call(rbind, lapply(tables, data.frame, stringsAsFactors=FALSE))

The data has '*' next to the numbers. I would like to isolate the numbers only. So instead of

52* 45* 67* 55*

I have

52 45 67 55

I have tried several methods to get the * special character out of 3rd through 8th columns and change the column to a numeric but since this character also has a meaning in R these are not working. I have tried:

x <- "~!@#$%^&*" 
str_replace_all(x, as.character(try[,3:8]), " ") 

I have also tried:

gsub("*","",try[,3:8])

The only function that has identified the * characters correctly is grep and grapl but I need another function that will use the grep output to remove the '*' special character.

grep('*',try)

Answer 1

Try this:

dat<-do.call(rbind, lapply(tables, data.frame, stringsAsFactors=FALSE))
dat[, -(1:2)] <- sapply(dat[, -(1:2)], function(col) {
  as.numeric(sub("[*]$", "", col))
})
head(dat)
# NEGERI...STATE                 KAWASAN.AREA MASA.TIME06.00AM MASA.TIME07.00AM MASA.TIME08.00AM MASA.TIME09.00AM MASA.TIME10.00AM MASA.TIME11.00AM
# NULL.1                Johor                  Kota Tinggi               52               53               52               50               50               49
# NULL.2                Johor                  Larkin Lama               51               51               51               NA               51               51
# NULL.3                Johor                         Muar               45               45               45               45               45               45
# NULL.4                Johor                 Pasir Gudang               56               56               55               56               56               56
# NULL.5                Kedah                   Alor Setar               50               50               50               50               50               49
# NULL.6                Kedah      Bakar Arang, Sg. Petani               NA               NA               NA               NA               NA               NA