dataframe - R data frame subsetting concepts -

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i have data frame called data. have column called colb na values , column called colc integer values , no nas.

when use subset syntax false results (all nas):

nrow(data[data$colb == "xxxx",])

but when run same syntax using function no results, expect , want.

data[which(data$colb== "xxxx"),]

also, when run following:

{data[data$colc == 185,]}

i correct result/output 1 matching row.

why this? having na in data? , subsetting column reference (instead of using subset function) without using not recommended?

na a logical constant of length 1 contains missing value indicator.

and e.g. which( c( na,na,na) ) returns 0 length integer vector none of comparisons can considered true, same if tried which( c(false,false,false) ). therefore trying subset data.frame nothing, returning nothing.

if need comparisons using data na values, use is.na(), function, e.g. consider:

x <- c( na , is.na(na) , na ) which( x ) #[1] 2

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