[R] NA rows appeared in data.frame

[Ernest Han]

Dear All,

After replacing some values in a data.frame, NAs rows have appeared
and cannot be removed. I have googled these issues and found that
several people have encountered it. Solutions in stackoverflow seem to
provide work-arounds but does not remove it from the data.frame.
Therefore, I am turning to experts in this community for help.

The code is as follows,

> t1 <- iris
> t1[t1$Petal.Width==1.8, "Petal.Width"] <- NA
> t1[t1$Petal.Width == 2.0, ]
      Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
NA              NA          NA           NA          NA      <NA>
NA.1            NA          NA           NA          NA      <NA>
NA.2            NA          NA           NA          NA      <NA>
NA.3            NA          NA           NA          NA      <NA>
111            6.5         3.2          5.1           2 virginica
114            5.7         2.5          5.0           2 virginica
NA.4            NA          NA           NA          NA      <NA>
122            5.6         2.8          4.9           2 virginica
123            7.7         2.8          6.7           2 virginica
NA.5            NA          NA           NA          NA      <NA>
NA.6            NA          NA           NA          NA      <NA>
NA.7            NA          NA           NA          NA      <NA>
NA.8            NA          NA           NA          NA      <NA>
132            7.9         3.8          6.4           2 virginica
NA.9            NA          NA           NA          NA      <NA>
NA.10           NA          NA           NA          NA      <NA>
148            6.5         3.0          5.2           2 virginica
NA.11           NA          NA           NA          NA      <NA>

## Twelve values were replaced, twelve NA rows appeared.

### MISC INFO ###
> sessionInfo()
R version 3.4.0 (2017-04-21)
Platform: x86_64-apple-darwin16.5.0 (64-bit)
Running under: macOS  10.14.2

Matrix products: default
BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libLAPACK.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] compiler_3.4.0 tools_3.4.0
> Sys.getlocale()
[1] "en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8"


Thank you,
Ernest