[R] basics on dataframes

From: Georg Ehret <georgehret_at_gmail.com>
Date: Sat, 05 Apr 2008 21:05:42 -0400


Dear R community,

    I am using a dataframe with lots of NAs and wish to create subsets from that dataframe. In the example below I intend to create a subset with all entries with V1>1. To my surprise the result also contains all entries with V1=NA. I would wish to learn more why this is or what I do wrong. I know that I can use the command "subset" and the NAs will not appear, but what is "wrong" with a[a$V1>1,]?
Thank you!
Georg.



Georg Ehret
Johns Hopkins
Baltimore, USA

> a

            V1        V2          V3         V4         V5
1           NA        NA          NA -2056.5981  0.8472496
2           NA        NA          NA  1407.8786  1.3349255
3           NA        NA          NA   579.2203  0.6082337
4           NA        NA          NA  1337.0740  1.0346453
5           NA        NA   -3.732253  -246.7270  1.9218894
6           NA -4.111501  -50.372053 -1512.2618 -0.8425137
7  100.0000000 -2.343761 -132.606282   101.7575  1.1870040
8   -1.8899018 11.921323   15.988519 -1199.5994  0.1907434
9 0.4819706 5.677561 29.677330 -200.9182 -0.1213408 10 -1.4981107 6.224487 209.133480 188.8852 -1.3321220
> b<-a[a$V1>1,]
> b
      V1        V2        V3       V4       V5
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
NA.4  NA        NA        NA       NA       NA
NA.5  NA        NA        NA       NA       NA
7 100 -2.343761 -132.6063 101.7575 1.187004

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