在这一部分中，仍然使用mtcars(Motor Trend Car Road Tests)这一数据集，以及mpg(one mile per gallon), hp(horsepower), wt(weight)这几个变量。
例01:
> vars<-c("mpg","hp","wt") > head(mtcars[vars]) mpg hp wt Mazda RX4 21.0 110 2.620 Mazda RX4 Wag 21.0 110 2.875 Datsun 710 22.8 93 2.320 Hornet 4 Drive 21.4 110 3.215 Hornet Sportabout 18.7 175 3.440 Valiant 18.1 105 3.460
1. 一些描述方法(a menagerie of methods)
例02：
> vars<-c("mpg","hp","wt") > summary(mtcars[vars]) mpg hp wt Min. :10.40 Min. : 52.0 Min. :1.513 1st Qu.:15.43 1st Qu.: 96.5 1st Qu.:2.581 Median :19.20 Median :123.0 Median :3.325 Mean :20.09 Mean :146.7 Mean :3.217 3rd Qu.:22.80 3rd Qu.:180.0 3rd Qu.:3.610 Max. :33.90 Max. :335.0 Max. :5.424
summary()函数：为数值变量提供最小值，最大值，均值，四分之一/四分之三值(quartiles)；
为因子(factor)和逻辑变量(logical vector)提供频率值(frequency)
例03：
> mystats<-function(x,na.omit=FALSE){ + if(na.omit) + x<-x[!is.na(x)] + m<-mean(x) + n<-length(x) + s<-sd(x) + skew<-sum((x-m)^3/s^3)/n + kurt<-sum((x-m)^4/s^4)/n-3 + return(c(n=n,mean=m,stdev=s,skew=skew,kurtosis=kurt)) + } >
> sapply(mtcars[vars],mystats) mpg hp wt n 32.000000 32.0000000 32.00000000 mean 20.090625 146.6875000 3.21725000 stdev 6.026948 68.5628685 0.97845744 skew 0.610655 0.7260237 0.42314646 kurtosis -0.372766 -0.1355511 -0.02271075
sapply(x,FUN,options)
· x：是数据帧(data frame)或矩阵(matrix);
· FUN：是任意函数(arbitrary function)，
典型的FUN函数包含mean,sd,var,min,max,median,length,range,quantile这些函数，skew,kurtosis则是需要自定义添加的。
注意：若想忽略掉缺省值(missing values)，则应该使用sapply(mtcars[vars],mystats,na.omit=TRUE)
例03（1）：
> mystats<-function(x,na.omit=TRUE){ + if(na.omit) + x<-x[!is.na(x)] + m<-mean(x) + n<-length(x) + s<-sd(x) + skew<-sum((x-m)^3/s^3)/n + kurt<-sum((x-m)^4/s^4)/n-3 + return(c(n=n,mean=m,stdev=s,skew=skew,kurtosis=kurt)) + } > sapply(mtcars[vars],mystats) mpg hp wt n 32.000000 32.0000000 32.00000000 mean 20.090625 146.6875000 3.21725000 stdev 6.026948 68.5628685 0.97845744 skew 0.610655 0.7260237 0.42314646 kurtosis -0.372766 -0.1355511 -0.02271075
扩展：一些用户描述的包也提供描述函数用于描述统计数据，如Hmisc，pastecs，psych，需要先安装，再使用。
例04：
> library(Hmisc) 载入需要的程辑包：survival 载入需要的程辑包：splines 载入需要的程辑包：Formula Hmisc library by Frank E Harrell Jr Type library(help='Hmisc'), ?Overview, or ?Hmisc.Overview') to see overall documentation. 载入程辑包：‘Hmisc’ 下列对象被屏蔽了from ‘package:survival’: untangle.specials 下列对象被屏蔽了from ‘package:base’: format.pval, round.POSIXt, trunc.POSIXt, units
> describe(mtcars[vars]) mtcars[vars] 3 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 ------------------------------------------------------------------------------------------------------------------------------------------------- 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 ------------------------------------------------------------------------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------------------------------------------------------------------------
Hmisc包中的describe()函数：返回自变量(variables)与因变量(observations)的数量，缺省值(missing)的数量以及特殊值(unique values)，平均值(mean)，quantile，五个最大值与五个最小值。
例05：
> install.packages("pastecs") trying URL 'http://cran.rstudio.com/bin/windows/contrib/3.0/pastecs_1.3-15.zip' Content type 'application/zip' length 1629764 bytes (1.6 Mb) opened URL downloaded 1.6 Mb package ‘pastecs’ successfully unpacked and MD5 sums checked The downloaded binary packages are in C:Usersseven-wangAppDataLocalTempRtmp8aVakLdownloaded_packages > library(pastecs) 载入需要的程辑包：boot 载入程辑包：‘boot’ 下列对象被屏蔽了from ‘package:survival’: aml > stat.desc(mtcars[vars]) mpg hp wt nbr.val 32.0000000 32.0000000 32.0000000 nbr.null 0.0000000 0.0000000 0.0000000 nbr.na 0.0000000 0.0000000 0.0000000 min 10.4000000 52.0000000 1.5130000 max 33.9000000 335.0000000 5.4240000 range 23.5000000 283.0000000 3.9110000 sum 642.9000000 4694.0000000 102.9520000 median 19.2000000 123.0000000 3.3250000 mean 20.0906250 146.6875000 3.2172500 SE.mean 1.0654240 12.1203173 0.1729685 CI.mean.0.95 2.1729465 24.7195501 0.3527715 var 36.3241028 4700.8669355 0.9573790 std.dev 6.0269481 68.5628685 0.9784574 coef.var 0.2999881 0.4674077 0.3041285
pastecs包中有函数stat.desc()：提供对统计数据的描述。
stat.desc(x,basic=TRUE,desc=TRUE,norm=FALSE,p=0.95)
·x：数据帧(data frame)或时间序列(time series);
·basic=TRUE(缺省状态)：各种值的个数，包括缺省值(missing value)，空值(null value)，最小值，最大值，值域(range)，和(sum).
·desc=TRUE(缺省状态)：提供中间值(median)，平均值(mean)，均值的标准错误(standard error of the mean)，95% confidence interval for the mean，variance，标准差(standard deviation)，coefficient of variation.
·norm=TRUE(非缺省状态)：返回正常的统计数据，包括skewness和kurtosis，以及它们的统计的重要性，the Shapiro-Wilk test of normality.
·p值的选项：用于计算the confidence interval for the mean(缺省状态默认为0.95 ).
例06：
> library(psych) > describe(mtcars[vars]) var n mean sd median trimmed mad min max range skew kurtosis se mpg 1 32 20.09 6.03 19.20 19.70 5.41 10.40 33.90 23.50 0.61 -0.37 1.07 hp 2 32 146.69 68.56 123.00 141.19 77.10 52.00 335.00 283.00 0.73 -0.14 12.12 wt 3 32 3.22 0.98 3.33 3.15 0.77 1.51 5.42 3.91 0.42 -0.02 0.17
psych包中的函数describe：提供不含缺失值的自变量(nonminssing observations)，平均值(mean)，标准差(standard deviation)，中间值(median)，边缘性均值(trimmed mean)，median absolute deviation，最大值，最小值，值域(range)，skew，kurtosis，the standard error of the mean.
注意：Hmics和psych包中都有decscribe()函数，一般使用最后载入的包中的函数。
2. 按组描述统计数
例07：
> aggregate(mtcars[vars],by=list(am=mtcars$am),mean) am mpg hp wt 1 0 17.14737 160.2632 3.768895 2 1 24.39231 126.8462 2.411000 > aggregate(mtcars[vars],by=list(am=mtcars$am),sd) am mpg hp wt 1 0 3.833966 53.90820 0.7774001 2 1 6.166504 84.06232 0.6169816
aggregate()函数：按组获得描述数据。
·有多于一组的变量，使用这样的代码：
by=list(name1=groupvar1,name2=groupvar2,......,nameN=groupvarN)
·仅允许使用单变量函数，如mean，standard deviation等。
例08（在RGui中完成的）：
> install.packages("doBy")
--- 在此連線階段时请选用CRAN的鏡子 --- also installing the dependencies ‘mvtnorm’, ‘multcomp’
试开URL’http://ftp.ctex.org/mirrors/CRAN/bin/windows/contrib/3.0/mvtnorm_0.9-9995.zip' Content type 'application/zip' length 222319 bytes (217 Kb) 打开了URL downloaded 217 Kb
试开URL’http://ftp.ctex.org/mirrors/CRAN/bin/windows/contrib/3.0/multcomp_1.2-19.zip' Content type 'application/zip' length 599099 bytes (585 Kb) 打开了URL downloaded 585 Kb
试开URL’http://ftp.ctex.org/mirrors/CRAN/bin/windows/contrib/3.0/doBy_4.5-8.zip' Content type 'application/zip' length 2606320 bytes (2.5 Mb) 打开了URL downloaded 2.5 Mb
程序包‘mvtnorm’打开成功，MD5和检查也通过 程序包‘multcomp’打开成功，MD5和检查也通过 程序包‘doBy’打开成功，MD5和检查也通过
下载的二进制程序包在
C:Usersseven-wangAppDataLocalTempRtmpEZL947downloaded_packages里
> library(doBy)
载入需要的程辑包：multcomp
载入需要的程辑包：mvtnorm
载入需要的程辑包：survival
载入需要的程辑包：splines
载入需要的程辑包：MASS
> summaryBy(mpg+hp+wt~am,data=mtcars,FUN=mystats)
am mpg.n mpg.mean mpg.stdev mpg.skew mpg.kurtosis hp.n hp.mean hp.stdev
1 0 19 17.14737 3.833966 0.01395038 -0.8031783 19 160.2632 53.90820
2 1 13 24.39231 6.166504 0.05256118 -1.4553520 13 126.8462 84.06232
hp.skew hp.kurtosis wt.n wt.mean wt.stdev wt.skew wt.kurtosis
1 -0.01422519 -1.2096973 19 3.768895 0.7774001 0.9759294 0.1415676
2 1.35988586 0.5634635 13 2.411000 0.6169816 0.2103128 -1.1737358
doBy包中的summarBy()函数：
summaryBy(formula,data=dataframe,FUN=function)
·formula：var1+var2+...+varN~groupvar1+groupvar2+...+groupvarM
其中～左边的是数值变量，右边的是分类好的变量。
例09（在RGui中完成）：
> install.packages("psych")
试开URL’http://ftp.ctex.org/mirrors/CRAN/bin/windows/contrib/3.0/psych_1.3.2.zip'
Content type 'application/zip' length 2555708 bytes (2.4 Mb)
打开了URL
downloaded 2.4 Mb
程序包‘psych’打开成功，MD5和检查也通过
下载的二进制程序包在
C:Usersseven-wangAppDataLocalTempRtmpEZL947downloaded_packages里
> library(psych)
> describeBy(mtcars[vars],mtcars$am)
group: 0
var n mean sd median trimmed mad min max range skew kurtosis se
mpg 1 19 17.15 3.83 17.30 17.12 3.11 10.40 24.40 14.00 0.01 -0.80 0.88
hp 2 19 160.26 53.91 175.00 161.06 77.10 62.00 245.00 183.00 -0.01 -1.21 12.37
wt 3 19 3.77 0.78 3.52 3.75 0.45 2.46 5.42 2.96 0.98 0.14 0.18
--------------------------------------------------------------------------
group: 1
var n mean sd median trimmed mad min max range skew kurtosis se
mpg 1 13 24.39 6.17 22.80 24.38 6.67 15.00 33.90 18.90 0.05 -1.46 1.71
hp 2 13 126.85 84.06 109.00 114.73 63.75 52.00 335.00 283.00 1.36 0.56 23.31
wt 3 13 2.41 0.62 2.32 2.39 0.68 1.51 3.57 2.06 0.21 -1.17 0.17
psych包中的describeBy()函数:提供对统计数据的描述。
·但是，该函数不适用于任何的一个函数，则有多组变量时需要写成
list(groupvar1,groupvar2,...,groupvarN)
并且仅当组间变量交叉时，没有空括号(no empty cells when the grouping variables are crossed)
例10：
> install.packages("reshape") trying URL 'http://cran.rstudio.com/bin/windows/contrib/3.0/reshape_0.8.4.zip' Content type 'application/zip' length 124891 bytes (121 Kb) opened URL downloaded 121 Kb package ‘reshape’ successfully unpacked and MD5 sums checked The downloaded binary packages are in C:Usersseven-wangAppDataLocalTempRtmpwj6VpMdownloaded_packages > library(reshape) 载入需要的程辑包：plyr 载入程辑包：‘reshape’ 下列对象被屏蔽了from ‘package:plyr’: rename, round_any > dstats<-function(x)(c(n=length(x),mean=mean(x),sd=sd(x))) > dfm<-melt(mtcars,measure.vars=c("mpg","hp","wt"),id.vars=c("am","cyl")) > cast(dfm,am+cyl+variable~.,dstats) am cyl variable n mean sd 1 0 4 mpg 3 22.900000 1.4525839 2 0 4 hp 3 84.666667 19.6553640 3 0 4 wt 3 2.935000 0.4075230 4 0 6 mpg 4 19.125000 1.6317169 5 0 6 hp 4 115.250000 9.1787799 6 0 6 wt 4 3.388750 0.1162164 7 0 8 mpg 12 15.050000 2.7743959 8 0 8 hp 12 194.166667 33.3598379 9 0 8 wt 12 4.104083 0.7683069 10 1 4 mpg 8 28.075000 4.4838599 11 1 4 hp 8 81.875000 22.6554156 12 1 4 wt 8 2.042250 0.4093485 13 1 6 mpg 3 20.566667 0.7505553 14 1 6 hp 3 131.666667 37.5277675 15 1 6 wt 3 2.755000 0.1281601 16 1 8 mpg 2 15.400000 0.5656854 17 1 8 hp 2 299.500000 50.2045815 18 1 8 wt 2 3.370000 0.2828427
reshape包，
dfm<-melt(dataframe,measure.vars=y,id.vars=g)
cast(dfm,groupvar1+groupvar2+...+variable~.,FUN)