[datatable-help] Can you explain what is going on???

[Frank Erickson]

Hi Gérald,

Your question is not really data.table specific, I think. Your
ttt[ttt == "0"] <- "O"
does not affect the result because you overwrite with
ttt <- ifelse(...
immediately afterwards. Maybe you meant to have ttt on the right-hand side
of the latter command, instead of membre.

--Frank


On Thu, May 14, 2015 at 10:04 AM, Gerald Jean <gerald.jean at dgag.ca> wrote:

>  Hello,
>
>
>
> the following code is extracted from a function where roughly 150
> variables of a large data set are transformed using data.table.
>
>
>
> The variable “membre” was coming out with one missing value, in trying to
> understand why, I extracted the code from the function, added a few “cat”
> statements and ran it directly in the terminal.
>
>
>
> ttt.test.sima[, ":="  (membre = {##
>
> +       cat(" Processing: membre", sep = "\n")
>
> +       ttt <- membre
>
> +       cat(paste(" Class ttt = ", class(ttt), sep = ""), sep = "\n")
>
> +       cat(paste(" Length ttt = ", length(ttt), sep = ""), sep = "\n")
>
> +       cat(paste(" sum(ttt == 0) = ", sum(ttt == "0"), sep = ""), sep =
> "\n")
>
> +       ttt[ttt == "0"] <- "O"  ## A few capital “O” are coded as zero “0”.
>
> +       cat(paste(" sum(ttt == 0) = ", sum(ttt == "0"), sep = ""), sep =
> "\n")
>
> +       ttt <- ifelse(PROV != " QC", " OAO",
>
> +                     ifelse(membre == "", " Ma  ", membre))
>
> +       cat(paste(" sum(ttt == 0) = ", sum(ttt == "0"), sep = ""), sep =
> "\n")
>
> +       merge.levels(factor(ttt, levels = c("O", "N", " Ma  ", " OAO"),
>
> +                           labels = c(" Oui", " Non", " Ma ", " OAO")),
>
> +                    k = list(" Oui" = c(" Oui", " OAO")))})]
>
> Processing: membre
>
> Class ttt = character
>
> Length ttt = 4750880
>
> sum(ttt == 0) = 2
>
> sum(ttt == 0) = 0
>
> sum(ttt == 0) = 1
>
>
>
> I don’t understand why after the « ifelse» statement the temporary
> variable « ttt» is back with a single « 0 (zero)» in it, resulting of
> course in the missing value of the factor created from it.
>
>
>
> Thanks for your support,
>
>
>
> Gérald
>
>
>
>     *Gerald Jean, M. Sc. en statistiques*
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