Using the built-in data
set air
quality
, fir
st load the data
and check what var
iables it contains:
data
(
air
quality
)
names
(
air
quality
)
Among ways to subset r
ows of a data
fr
ame
in S language, ther
e ar
e two usual appr
oaches. Either
you delete
r
ows by extr
acting all other
r
ows of the data
fr
ame
using a vector
of logical values, or
you r
emove these r
ows using a vector
of negative indices.
Assume that days 5 and 7 in May of the air
quality
measur
ements ar
e outlier
s and you want to r
epeat an analysis without these r
ows. You wr
ite:
length
(
air
quality
$Day
)
air
quality2
<- subset
(
air
quality
, !(
Day %in% c
(
5
, 7
)
& Month
== 5
)
)
length
(
air
quality2
$Day
)
Similar
ly, you can delete
specific r
ows. In or
der
to delete
lines 2 and 7, you wr
ite:
length
(
air
quality
$Day
)
air
quality3
<- air
quality
[
-c
(
2
, 7
)
, ]
length
(
air
quality3
$Day
)
— Claudia Beleites
2008/01/02
Be car
eful with logical ver
sus
numer
ic index vector
s:
new
.data
<- data
[
!outlier
s
, ]
# logical indices
new
.data
<- data
[
-outlier
s
, ]
# numer
ic indices
Using the numer
ic for
m for
a logical index vector
will delete
the fir
st r
ow only:
>
data
<- 1
:10
>
outlier
s
<- data
%in% 3
:7
>
new
.data
<- data
[
!outlier
s
]
# (desir
ed effect)
>
new
.data
[1] 1 2 8 9 10
>
new
.data
<- data
[
-outlier
s
]
# (wr
ong code)
>
new
.data
[1] 2 3 4 5 6 7 8 9 10
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