[R] Converting chr to num

[Daniel Nordlund]

See comment inline below:

On 8/18/2018 10:06 PM, Rui Barradas wrote:
> Hello,
> 
> It also works with class "factor":
> 
> df <- data.frame(variable = c("12.6%", "30.9%", "61.4%"))
> class(df$variable)
> #[1] "factor"
> 
> as.numeric(gsub(pattern = "%", "", df$variable))
> #[1] 12.6 30.9 61.4
> 
> 
> This is because sub() and gsub() return a character vector and the 
> instruction becomes an equivalent of what the help page ?factor 
> documents in section Warning:
> 
> To transform a factor f to approximately its original numeric values, 
> as.numeric(levels(f))[f] is recommended and slightly more efficient than 
> as.numeric(as.character(f)).
> 
> 
> Also, I would still prefer
> 
> as.numeric(sub(pattern = "%$","",df$variable))
> #[1] 12.6 30.9 61.4
> 
> The pattern is more strict and there is no need to search&replace 
> multiple occurrences of '%'.

The pattern is more strict, and that could cause the conversion to fail 
if the process that created the strings resulted in trailing spaces. 
Without the '$' the conversion succeeds.

df <- data.frame(variable = c("12.6% ", "30.9%", "61.4%"))
as.numeric(sub('%$', '', df$variable))
[1]   NA 30.9 61.4
Warning message:
NAs introduced by coercion


<<<snip>>>


Dan

-- 
Daniel Nordlund
Port Townsend, WA  USA