On Jul 18, 2010, at 12:02 PM, stephen sefick wrote:
I am confused by the behavior of the below piece of code. The NAs are
making it past the logical call ==0. I am sure that I am missing
something. I just don't understand this behavior. Thanks for your
help in advance.
########code#######################################################
left <- (structure(list(measurment_num = c(2, 2.2, 2.4, 2.6, 2.8,
2.82,
3, NA, NA, NA), bankfull_depths_m = c(1.29, 1.28, 1.23, 0.18,
-0.05, 0, -0.09, NA, NA, NA)), .Names = c("measurment_num",
"bankfull_depths_m"
), row.names = c(10L, 11L, 12L, 13L, 14L, 20L, 15L, 16L, 17L,
18L), class = "data.frame"))
if(sum(left[,"bankfull_depths_m"]==0, na.rm=TRUE) == 1){
left_min <- left[left[,"bankfull_depths_m"]==0, "measurment_num"]
}
left
Why aren't you looking at left_min? That is what the code is supposed
to be changing. I do not get an error and left_min[1] (now) =='s 2.82.
Regarding why there are the 3 NA's, ... you need to look at the
documentation for Extract in the section very appropriately entitled:
"NAs in indexing"
I have been bitten by that behavior more times than I care to admit
and I am not the only person that thinks that aspect of the R language
is badly designed. See Aniko Szabo's comments:
http://radfordneal.wordpress.com/2008/09/21/design-flaws-in-r-3-%E2%80%94-zero-subscripts/
The problem is in data.frame[ and any NA in a logical vector will
return a row of NA's. This can be avoid by wrapping which() around the
logical vector which seems entirely wasteful or using subset().
David Winsemius, MD
West Hartford, CT
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