[R] y2z question (AGD)

[David L Carlson]

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

______________________________________________
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.