이 절에서는 1974년에 미국의 모터 트렌드 잡지에 실린 1973 ~ 1974년 자동차 모델의 연료 소비, 10가지 디자인 요소, 성능을 비교한 mtcars 데이터에 대해 요약해본다. 다음은 mtcars 데이터의 모양이다.
> str(mtcars)
'data.frame': 32 obs. of 11 variables:
$ mpg : num 21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
$ cyl : num 6 6 4 6 8 6 8 4 4 6 ...
$ disp: num 160 160 108 258 360 ...
$ hp : num 110 110 93 110 175 105 245 62 95 123 ...
$ drat: num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
$ wt : num 2.62 2.88 2.32 3.21 3.44 ...
$ qsec: num 16.5 17 18.6 19.4 17 ...
$ vs : num 0 0 1 1 0 1 0 1 1 1 ...
$ am : num 1 1 1 0 0 0 0 0 0 0 ...
$ gear: num 4 4 4 3 3 3 3 4 4 4 ...
$ carb: num 4 4 1 1 2 1 4 2 2 4 ...
이 데이터에 describe( )를 적용해보자. describe( )는 summary( )와 유사하지만 결측치의 수(missing), 서로 다른 값의 수(unique), 데이터의 분포, 합, 평균 등 좀 더 다양한 요약 정보를 제시한다.
> describe(mtcars)
mtcars
11 Variables 32 Observations
------------------------------------------------------------------------------------
mpg
n missing unique Mean .05 .10 .25 .50 .75 .90 .95
32 0 25 20.09 12.00 14.34 15.43 19.20 22.80 30.09 31.30
lowest : 10.4 13.3 14.3 14.7 15.0, highest: 26.0 27.3 30.4 32.4 33.9
------------------------------------------------------------------------------------
cyl
n missing unique Mean
32 0 3 6.188
4 (11, 34%), 6 (7, 22%), 8 (14, 44%)
------------------------------------------------------------------------------------
disp
n missing unique Mean .05 .10 .25 .50 .75 .90 .95
32 0 27 230.7 77.35 80.61 120.83 196.30 326.00 396.00 449.00
lowest : 71.1 75.7 78.7 79.0 95.1, highest: 360.0 400.0 440.0 460.0 472.0
------------------------------------------------------------------------------------
hp
n missing unique Mean .05 .10 .25 .50 .75 .90 .95
32 0 22 146.7 63.65 66.00 96.50 123.00 180.00 243.50 253.55
lowest : 52 62 65 66 91, highest: 215 230 245 264 335
------------------------------------------------------------------------------------
drat
n missing unique Mean .05 .10 .25 .50 .75 .90 .95
32 0 22 3.597 2.853 3.007 3.080 3.695 3.920 4.209 4.314
lowest : 2.76 2.93 3.00 3.07 3.08, highest: 4.08 4.11 4.22 4.43 4.93
------------------------------------------------------------------------------------
wt
n missing unique Mean .05 .10 .25 .50 .75 .90 .95
32 0 29 3.217 1.736 1.956 2.581 3.325 3.610 4.048 5.293
lowest : 1.513 1.615 1.835 1.935 2.140, highest: 3.845 4.070 5.250 5.345 5.424
------------------------------------------------------------------------------------
qsec
n missing unique Mean .05 .10 .25 .50 .75 .90 .95
32 0 30 17.85 15.05 15.53 16.89 17.71 18.90 19.99 20.10
lowest : 14.50 14.60 15.41 15.50 15.84, highest: 19.90 20.00 20.01 20.22 22.90
------------------------------------------------------------------------------------
vs
n missing unique Sum Mean
32 0 2 14 0.4375
------------------------------------------------------------------------------------
am
n missing unique Sum Mean
32 0 2 13 0.4062
------------------------------------------------------------------------------------
gear
n missing unique Mean
32 0 3 3.688
3 (15, 47%), 4 (12, 38%), 5 (5, 16%)
------------------------------------------------------------------------------------
carb
n missing unique Mean
32 0 6 2.812
1 2 3 4 6 8
Frequency 7 10 3 10 1 1
% 22 31 9 31 3 3
------------------------------------------------------------------------------------
>
같은 데이터에 summary( )를 적용한 결과는 다음과 같다.
> summary(mtcars)
mpg cyl disp hp drat
Min. :10.40 Min. :4.000 Min. : 71.1 Min. : 52.0 Min. :2.760
1st Qu.:15.43 1st Qu.:4.000 1st Qu.:120.8 1st Qu.: 96.5 1st Qu.:3.080
Median :19.20 Median :6.000 Median :196.3 Median :123.0 Median :3.695
Mean :20.09 Mean :6.188 Mean :230.7 Mean :146.7 Mean :3.597
3rd Qu.:22.80 3rd Qu.:8.000 3rd Qu.:326.0 3rd Qu.:180.0 3rd Qu.:3.920
Max. :33.90 Max. :8.000 Max. :472.0 Max. :335.0 Max. :4.930
wt qsec vs am gear
Min. :1.513 Min. :14.50 Min. :0.0000 Min. :0.0000 Min. :3.000
1st Qu.:2.581 1st Qu.:16.89 1st Qu.:0.0000 1st Qu.:0.0000 1st Qu.:3.000
Median :3.325 Median :17.71 Median :0.0000 Median :0.0000 Median :4.000
Mean :3.217 Mean :17.85 Mean :0.4375 Mean :0.4062 Mean :3.688
3rd Qu.:3.610 3rd Qu.:18.90 3rd Qu.:1.0000 3rd Qu.:1.0000 3rd Qu.:4.000
Max. :5.424 Max. :22.90 Max. :1.0000 Max. :1.0000 Max. :5.000
carb
Min. :1.000
1st Qu.:2.000
Median :2.000
Mean :2.812
3rd Qu.:4.000
Max. :8.000