如何使用describe.by生成五个数字摘要

Question

I wonder how to call for five-number stats from describeBy() function as provided by summary() . After calling library(psych) , the current function reports min, max and median, but not stats for 25th and 75th quartiles.

attach(mtcars)
describeBy(mpg, gear)

var  n  mean   sd median trimmed  mad  min  max range  skew kurtosis   se 

Appreciate your help in advance.

Answer 1

There is also a built-in base function specifically for the five numbers unsurprisingly called: fivenum

aggregate(mpg ~ gear, data=mtcars, fivenum)
  gear mpg.1 mpg.2 mpg.3 mpg.4 mpg.5
1    3 10.40 14.50 15.50 18.40 21.50
2    4 17.80 21.00 22.80 28.85 33.90
3    5 15.00 15.80 19.70 26.00 30.40

EDIT to answer the followup Q in comments (as I interpret it) you can use the . in the formula to specify all other columns

aggregate(.~gear, data=mtcars, fivenum)
#too wide to print here

Or if you just want the fivenum for all columns without the gear split then that is:

    apply(mtcars, 2,fivenum)
       mpg cyl   disp  hp  drat     wt   qsec vs am gear carb
[1,] 10.40   4  71.10  52 2.760 1.5130 14.500  0  0    3    1
[2,] 15.35   4 120.65  96 3.080 2.5425 16.885  0  0    3    2
[3,] 19.20   6 196.30 123 3.695 3.3250 17.710  0  0    4    2
[4,] 22.80   8 334.00 180 3.920 3.6500 18.900  1  1    4    4
[5,] 33.90   8 472.00 335 4.930 5.4240 22.900  1  1    5    8