r - 对数据框属性的逻辑测试如何导致 NA 行

Question

我有一个如下形式的数据框:

>df
stationid    station      gear sample     lat    lon       date depth
1     25679          CORBOX150    UE4 53.9015 7.8617 15.07.1987    19
2     25681 UE9 Kern CORCRB050    UE9 54.0167 7.3982 15.07.1987    33
3        NA                           54.0167 7.3982 15.07.1987    33

对 stationid 的逻辑测试在正确的第一行旁边，给了我一条充满 NA 的烦人行:

> df[df$stationid=="25679",]
stationid station      gear sample     lat    lon       date depth
1      25679         CORBOX150    UE4 53.9015 7.8617 15.07.1987    19
NA        NA    <NA>      <NA>   <NA>      NA     NA       <NA>    NA

为什么？

在 df 第 3 行的某处，事情变得一团糟，我想。

数据如下:

df<-structure(list(stationid = c(25679L, 25681L, NA), station = structure(c(2L, 
3L, 1L), .Label = c("", " ", "UE9 Kern"), class = "factor"), 
gear = structure(c(2L, 3L, 1L), .Label = c("", "CORBOX150", 
"CORCRB050"), class = "factor"), sample = structure(c(2L, 
3L, 1L), .Label = c("", "UE4", "UE9"), class = "factor"), 
lat = c(53.9015, 54.0167, 54.0167), lon = c(7.8617, 7.3982, 
7.3982), date = structure(c(1L, 1L, 1L), .Label = "15.07.1987", class = "factor"), 
depth = c(19L, 33L, 33L)), .Names = c("stationid", "station", 
"gear", "sample", "lat", "lon", "date", "depth"), class = "data.frame", row.names = c(NA, 
-3L))

Answer 1

与 NA 的任何比较导致 NA 的结果(见 http://cran.r-project.org/doc/manuals/R-intro.html#Missing-values )......你可以使用

df[df$stationid==25679 & !is.na(df$stationid),]

或(如上面评论中所建议的)

df[which(df$stationid==25679),] 

或

subset(df,stationid==25679)

( subset 有时会产生不必要的副作用，即删除 NA 值，但在这种情况下，这正是您想要的)