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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