[R] y2z question (AGD)

William Dunlap wdunlap at tibco.com
Mon Oct 26 19:45:36 CET 2015


You can also use the na.exclude function, which is like na.omit but attaches
an attribute, "na.action", telling which rows were removed.  Then use the
naresid function to insert NA's into the right places in the output of
the function
that only works properly on NA-less data.  E.g.,

cleanData <- na.exclude(data)
data$zeta <- naresid(attr(cleanData, "na.action"), with(cleanData,
y2z(weight, age/12, sex, ref=who.wgt)))
data
#  sex weight age   zeta
#1   M    8.5   8 -0.124
#2   M    8.2   9 -0.751
#3   M    9.0  12 -0.635
#4   F     NA   9     NA
#5   M    5.8   1  2.002

It is a little wordy, but it does handle both vector and matrix data.

Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Sun, Oct 25, 2015 at 10:53 AM, David L Carlson <dcarlson at tamu.edu> wrote:
> It looks like the y2z() function strips NA's so that the vector lengths do not match any longer. The simplest workaround is to remove the NA's. You could do that by using data2 <- na.omit(data) to strip the observations with NA if they will not be used in the rest of the analysis.
>
> If you want to preserve the NAs in the data frame, this seems to work:
>
>> nomiss <- complete.cases(data)
>> data$zeta[nomiss] <- with(data[nomiss, ], y2z(weight, age/12, sex, ref=who.wgt))
>> data
>   sex weight age   zeta
> 1   M    8.5   8 -0.124
> 2   M    8.2   9 -0.751
> 3   M    9.0  12 -0.635
> 4   F     NA   9     NA
> 5   M    5.8   1  2.002
>
>
> David L. Carlson
> Department of Anthropology
> Texas A&M University
>
>
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Martin Canon
> Sent: Sunday, October 25, 2015 7:03 AM
> To: R help <r-help at r-project.org>
> Subject: [R] y2z question (AGD)
>
> Hi to all.
>
> I've been trying to calculate weight-for-age z-scores with the y2z
> command (AGD package).
>
> However, I keep getting strange results.
>
> My hypothesis is that missings are the problem.
>
> My dataframe looks like this:
>
> data <- structure(list(sex = structure(c(3L, 3L, 3L, 2L, 3L), .Label = c("",
> "F", "M"), class = "factor"), weight = c(8.5, 8.2, 9, NA, 5.8),
>     age = c(8, 9, 12, 9, 1)), .Names = c("sex", "weight", "age"
> ), class = "data.frame", row.names = c(NA, 5L))
>
> Weight is in kg and age in months.
> I will use WHO curves for children younger than 2 years of age.
>
> z-score calculation:
>
> library(AGD)
> data$zeta <- y2z(y = data$weight, x = data$age/12, sex = data$sex,
>                 ref = get("who.wgt"))
>
> I get:
>
> Warning message:
> In `split<-.default`(`*tmp*`, f, drop = drop, value = value) :
>   number of items to replace is not a multiple of replacement length
>
> data$zeta
> [1]     NA     NA     NA -0.124     NA
>
> However a for loop seems to work.
>
> for (i in 1:5) {
>
>   data$zeta[i] <- y2z(y = data$weight[i],
>                  x = data$age[i]/12,
>                  sex = data$sex[i],
>                 ref = get("who.wgt"))
> }
>
> data$zeta
> [1] -0.124 -0.751 -0.635     NA  2.002
>
> Is there a workaround so that I don't have to use a for loop?
> na.action doesn't work either.
>
> Thanks.
>
>
> Martin
>
> ______________________________________________
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>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



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