I have a data frame and I am trying to convert class of each variable of dt based on col_type.
Find example below for more detail.
> dt
id <- c(1,2,3,4)
a <- c(1,4,5,6)
b <- as.character(c(0,1,1,4))
c <- as.character(c(0,1,1,0))
d <- c(0,1,1,0)
dt <- data.frame(id,a,b,c,d, stringsAsFactors = FALSE)
> str(dt)
'data.frame': 4 obs. of 5 variables:
$ id: num 1 2 3 4
$ a : num 1 4 5 6
$ b : chr "0" "1" "1" "4"
$ c : chr "0" "1" "1" "0"
$ d : num 0 1 1 0
Now, I am trying to convert class of each column based on below data frame.
> var
var <- c("id","a","b","c","d")
type <- c("character","numeric","numeric","integer","character")
col_type <- data.frame(var,type, stringsAsFactors = FALSE)
> col_type
var type
1 id character
2 a numeric
3 b numeric
4 c integer
5 d character
I want to convert id to class mention in col_type data frame and so on for all other columns.
My Attempts:
setDT(dt)
for(i in 1:ncol(dt)){
if(colnames(dt)[i]%in%col_type$var){
a <- col_type[col_type$var==paste0(intersect(colnames(dt)[i],col_type$var)),]
dt[,col_type$var[i]:=eval(parse(text = paste0("as.",col_type$type[i],"(",col_type$var[i],")")))]
}
}
Note- My solution works but it is really slow and I am wondering if I can do it more efficiently and cleanly.
Suggestions will be appreciated.
I would read the data in with the colClasses
argument derived from the col_type
table:
library(data.table)
library(magrittr)
setDT(col_type)
res = capture.output(fwrite(dt)) %>% paste(collapse="\n") %>%
fread(colClasses = col_type[, setNames(type, var)])
str(res)
Classes ‘data.table’ and 'data.frame': 4 obs. of 5 variables:
$ id: chr "1" "2" "3" "4"
$ a : num 1 4 5 6
$ b : num 0 1 1 4
$ c : int 0 1 1 0
$ d : chr "0" "1" "1" "0"
- attr(*, ".internal.selfref")=<externalptr>
If you can do this when the data is read in initially, it simplifies to...
res = fread("file.csv", colClasses = col_type[, setNames(type, var)])
It's straightforward to do all of this without data.table.
If somehow the data is never read into R (received as RDS?), there's:
setDT(dt)
res = dt[, Map(as, .SD, col_type$type), .SDcols=col_type$var]
str(res)
Classes ‘data.table’ and 'data.frame': 4 obs. of 5 variables:
$ id: chr "1" "2" "3" "4"
$ a : num 1 4 5 6
$ b : num 0 1 1 4
$ c : int 0 1 1 0
$ d : chr "0" "1" "1" "0"
- attr(*, ".internal.selfref")=<externalptr>
See showMethods("coerce")
as some conversions might fail, e.g.: as(letters[1:3], "factor")