NAs introduced by coercion

Hallo,

i get a warning message that NAs are introduced by coercion,
so my idea is to write a function to see which values are turned into
NA 

For this i need to write a function to go through (loop) the original
data and the transformed (with the introduced na) to see which data were
transformed to NA.
So the return of this function should be a 2*many matrix like structure,
eg
names: indexolddata, valueolddata
45, 789
89, 4568
and so on
(on the data that were transformed into an NA)

I am doing something wrong.

A simple example:

test2 <- function(d) {

+ v <- vector()
+ for (i in 1:length(d)) {
+
e.csv
.RData
.Rhistory
+ append(v, i , after=i)
+
e.csv
.RData
.Rhistory
+ }
+ v
+        }

# why a get file listing running this code, no idea, anyway i continue

temp <- test2(data)
temp

logical(0)

# so no data?
# but ..

length(data)

[1] 3240

What am i doing wrong?
Thank u.