R面向的数据类型
数据描述：在一年时间内，收集河流水样。测定它们的化学性质和7种有害藻类（a1-a7）的存在频率
求：预测藻类模型，了解影响藻类的因素。
1. 数据准备
rm(list = ls()) #删除先前存档的一些环境变量，打扫干净屋子再请客
if(!require('DMwR'))(
install.packages('DMwR')
)
data(algae)
#查看数据集的基本情况
head(algae)
summary(algae)
str(algae)
图.1
图.2
从图.1可以看出，数据中存在缺失值和异常值
从图.2可以看出，该数据有三个因子型变量'season'，'size'，'speed'，其余为数值型变量
2. 初步可视化
2.1 观察各个变量数据的规范性
几乎每个变量都有异常值存在，多是异常大值
par(mfrow = c(3,5)) #将成图区域设定为3行5列的形式，同时呈现多张图片
for(i in 4:18){ #这里只针对数值型变量
boxplot(algae[,i],xlab = names(algae)[i])
}
par(mfrow = c(1,1)) #返回默认设置
图.3
2.2 观察变量间的相关性
library('PerformanceAnalytics')
chart.Correlation(algae[,4:18], histogram=TRUE,pch='+') #'图.4'
library('dplyr')
library('Hmisc')
#计算各个数值型变量间的相关性及显著性，与'chart.Correlation'不同，这里可以获得相关性数据
res <- algae[,4:18] %>% as.matrix() %>% rcorr(type = 'pearson')
library('corrplot')
corrplot(res$r, p.mat = res$P, type = "upper", order = "hclust", tl.col = "black", tl.srt = 45)#'图.5'
图.4
图.5
2.3 双变量间的相关性
由上可知，"oPO4"和"PO4"高度相关，达到0.91
library("ggpubr")
ggscatter(algae, x = "oPO4", y = "PO4",
facet.by = 'season',scales ='free', #注释此行，则展现全局下两个变量的相关性
size = 3,color = 'black', #定义点的属性
add.params = list(color = 'red', lty = 2, lwd = 2), #定义拟合曲线的属性
add = "reg.line", conf.int = TRUE, #添加拟合曲线和置信区间
cor.coef = TRUE, cor.method = "pearson",cor.coef.size = 5, #添加拟合参数
xlab = "oPO4", ylab = "PO4")
图.6
2.4 观察单个变量的数据分布情况
- 绘制频率分布直方图和正态分布图
library('car')
par(mfrow=c(1,2))
hist(algae$mxPH, prob=T, xlab='', main='Histogram of maximum pH value',ylim=0:1) #绘制频率分布直方图
lines(density(algae$mxPH,na.rm=T),col='blue')#在直方图之上，叠加频率密度曲线
rug(jitter(algae$mxPH),col = 'blue') #在直方图的横坐标轴上添加须线，表征数据在坐标轴上分布的密集度
qqPlot(algae$mxPH,main='Normal QQ plot of maximum pH',col.lines = 'purple') #另外绘制正态分布图
par(mfrow=c(1,1))
图.7
- 绘制单变量箱线图，展示数据分布情况
boxplot(algae$oPO4,ylab='Orthophosphate (oPO4)',notch = T)
rug(jitter(algae$oPO4),side=2)#'side = 2'表示在y轴绘制须线表征数据分布密集度
abline(h=mean(algae$oPO4,na.rm=T),lty=2,col = 'red')#添加均值线
abline(h=median(algae$oPO4,na.rm=T),lty=2,col = 'blue')#添加中值线
abline(h=quantile(algae$oPO4,0.25,na.rm=T),lty=2,col = 'pink')#添加1/4分位线
abline(h=quantile(algae$oPO4,0.75,na.rm=T),lty=2,col = 'purple')#添加3/4分位线
图.8
- 手动挑选异常值，并定位其在数据中的位置
plot(algae$NH4,xlab='')
abline(h=mean(algae$NH4,na.rm=T),lty=1,col = 'red')
abline(h=mean(algae$NH4,na.rm=T)+sd(algae$NH4,na.rm=T),lty=2,col= 'green')
abline(h=median(algae$NH4,na.rm=T),lty=3,col='blue')
# 手动挑选异常值，鼠标点击多个点，即可获得该点在数据中的索引即行号
identify(algae$NH4)
algae[c(20,34,35,88,89,133,153),'NH4']
图.9
- 考察变量在某一分组内的分布情况
library(lattice)
bwplot(size ~ a1, data=algae,ylab='River Size',xlab='Algal A1')
library(Hmisc)
bwplot(size ~ a1, data=algae,panel=panel.bpplot,
probs=seq(.01,.49,by=.01), datadensity=TRUE,
ylab='River Size',xlab='Algal A1')
左图可明显判断异常值的存在，右图可展现数据在不同范围内的分布集中度
图.10
- 考察变量在多个分组内的分布情况
- 分组因素均为因子型变量
histogram(~ mxPH | season,data=algae)
algae$season <- factor(algae$season,levels=c('spring','summer','autumn','winter'))
histogram(~ mxPH | size*speed,data=algae)
stripplot(size ~ mxPH | speed, data=algae, jitter=T)
- 既有因子型变量，还有数值型变量，需将数值型变量离散化，转换为因子类型
minO2 <- equal.count(na.omit(algae$mnO2),
number=3,overlap=1/10)# number设置区间个数，overlap设置区间靠近边界的重合。
stripplot(season ~ a3|minO2,scales = 'free',
data=algae[!is.na(algae$mnO2),],
strip = strip.custom(strip.names = TRUE, strip.levels = TRUE))
图.11
3. 数据中存在缺失值，下面我们对其进行处理
3.1 了解缺失值的基本分布情况
library('mice')
md.pattern(algae,rotate.names = T) #可视化缺失值，以红色表示缺失值
#分别统计各行各列缺失值的分布情况
apply(algae,1,function (x) sum(is.na(x)))
apply(algae,2,function(x) sum(is.na(x)))
图.12
3.2 直接删除缺失值，在缺失值占比很少的情况采用
- 对全局或特定变量，删除包含NA的行
# 获取包含缺失值的行
algae.na <- algae[!complete.cases(algae),]
md.pattern(algae.na,rotate.names = T)
nrow(algae.na)
#获取不含缺失值的行
algae.clean <- na.omit(algae) #同algae <- algae[complete.cases(algae),]
md.pattern(algae.clean,rotate.names = T)
nrow(algae.clean)
#设定阈值，返回缺失值占比超过该阈值的行
manyNAs(algae,0.2)
algae <- algae[-manyNAs(algae),]
# 对某一变量，使用有效值的均值或者中值等进行填充
algae[48,'mxPH'] <- mean(algae$mxPH,na.rm=T) #针对某一行
algae[is.na(algae$Chla),'Chla'] <- median(algae$Chla,na.rm=T) #针对所有包含缺失值的行
3.3 基于一定的规则填充缺失值
- 针对全局填充
library('dplyr')
algae.Imp <- algae %>% impute(fun = median) #alternative "fun = mean",or "fun = 0.4"
algae.ctrl <- algae %>% centralImputation() #如果是数值型变量，使用中位数；如果是字符型变量，使用众数
algae.knn <- algae %>% knnImputation(k = 5, meth = 'weighAvg') #使用欧氏距离找到与之最近的数值，取加权平均值
library('randomForest')
algae.rf <- rfImpute(season ~ .,algae,iters = 6, ntree = 300) # response vector must has no NAs
- 根据变量间相关性进行填值
algae <- algae[-manyNAs(algae),]
# 将各变量间的相关性以符号表示，发现"oPO4"和"PO4"相关性较高
algae[,4:18] %>% cor(use = 'complete.obs') %>% symnum()
lm(PO4 ~ oPO4,data=algae)#对两变量进行线性回归，以回归参数进行填值
algae[28,'PO4'] <- 42.897 + 1.293 * algae[28,'oPO4']
data(algae)
algae <- algae[-manyNAs(algae),]
fillPO4 <- function(oP) {
if (is.na(oP))
return(NA)
else
return(42.897 + 1.293 * oP)
}
algae[is.na(algae$PO4),'PO4'] <-
sapply(algae[is.na(algae$PO4),'oPO4'],fillPO4)
4. 聚类分析
#清空当前工作环境，重新加载数据
rm(list = ls())
require('DMwR')
data("algae")
4.1 数据准备和聚类预览
#聚类分析对缺失值及其敏感，以kmeans均值方法填充缺失值
algae.knn <- algae %>% knnImputation(k = 10, meth = 'weighAvg') #使用欧氏距离找到与之最近的数值，取加权平均值
#初步判断数据大概可以聚为几类
if(!require('factoextra'))(
install.packages('factoextra')
)
fviz_nbclust(algae.knn[,-c(1:3)],kmeans,method = 'wss') + #'wss' within sum of squares
geom_vline(xintercept = 4, lty = 2)#
初步判断，可分为4组
图.13
4.2 层次聚类
dis = dist(algae.knn[,-c(1:3)],method = 'euclidean')
dis_hc = hclust(dis,method = 'ward.D2')
library('scales');show_col(hue_pal()(4))# 展示ggplot2默认的一些颜色
fviz_dend(dis_hc, k=4, cex = 0.5, color_labels_by_k = T, rect = F,
k_colors = c('#F8766D','#A3A500','#0087BF7D','#00B0F6'))
# 很明显，聚类效果很差，有偏离点存在
图.14
4.3 kmeans均值聚类 (1)
library('ggfortify')
autoplot(kmeans(algae.knn[,4:18], 4),data = algae.knn, size = 3, label = F,
label.size = 4,frame = T,frame.type = 't')# 很明显，聚类效果很差
图.15
4.3 kmeans均值聚类 (2)
# 变量太多，不适合此种展现形式
# if(!require('GGally'))(
# install.packages('GGally')
# )
# rest = kmeans(algae.knn[,-(1:3)],centers = 4)
# ggpairs(algae.knn[,-(1:3)], cex = 0.5,mapping = aes(color = as.character(rest$cluster)))
# 同样的，聚类效果很差
# 变量较多情况下，从全局出发考查属性间的差异性
if(!require(flexclust))(
install.packages("flexclust")
)
clk4 <- cclust(algae.knn[,-c(1:3)], k=4);clk4
barchart(clk4,legend=TRUE)
# 同样的，聚类效果很差,原因在于有异常值存在
图.16
4. 处理异常值
4.1 盖帽法处理异常值
即分别设定数据的上下限，高于上限的用上限替换，低于下限的用下限替换
#清空当前工作环境，重新加载数据
rm(list = ls())
require('DMwR')
data(algae)
#使用kmeans均值算法对填充缺失值
clean_algae = knnImputation(algae, k = 10)
# 定义一个函数，对一个数值型变量，使用1%处的数值替换小于1%的异常小值，使用90%处的数值替换大于90%的异常大值
block = function(x,lower = T, upper = T){
if(lower){
q1 <- quantile(x,0.01)
x[x<=q1] = q1
}
if(upper){
q90 <- quantile(x,0.90)
x[x>=q90] = q90
}
return(x)
}
对所有数值型变量执行盖帽法替换异常值
clean_algae_blk = sapply(clean_algae[,-c(1:3)],block) %>% cbind(clean_algae[,1:3],.)
4.2 盖帽法处理异常值后重现考察数据的分布情况
- 箱线图展示数据的分布情况
clean_algae_blk %>% melt() %>%
ggplot(aes(NULL,value)) +
labs(x = '',y ='') +
geom_boxplot(aes(fill = variable),show.legend = F) +
facet_wrap(variable ~. , scales = 'free_y')
图.17
- 重新聚类
if(!require('factoextra'))(
install.packages('factoextra')
)
#处理异常值之后，初步评估数据聚为5组
fviz_nbclust(clean_algae_blk[,-c(1:3)],kmeans,method = 'wss') + #'wss' within sum of squares
geom_vline(xintercept = 5, lty = 2)#
dis = dist(clean_algae_blk[,-c(1:3)],method = 'euclidean')
dis_hc = hclust(dis,method = 'ward.D2')
library('scales');show_col(hue_pal()(5))# 展示ggplot2默认的一些颜色
#层次聚类，处理异常值后，聚类效果显著改善
fviz_dend(dis_hc, k=5, cex = 0.5, color_labels_by_k = T, rect = F,
k_colors = c('#F8766D','#A3A500','#0087BF7D','#00B0F6','#E76BF3'))
#kmeans均值聚类效果显著改善
library('ggfortify')
autoplot(kmeans(clean_algae_blk[,4:18], 5),data = clean_algae_blk, size = 3, label = F,
label.size = 4,frame = T,frame.type = 't')
# 变量太多，不适合此种展现形式
# if(!require('GGally'))(
# install.packages('GGally')
# )
# rest = kmeans(clean_algae_blk[,-(1:3)],centers = 5)
# ggpairs(clean_algae_blk[,-(1:3)], cex = 0.5,mapping = aes(color = as.character(rest$cluster)))
#变量较多情况下，更应注重考查整体的数据分类情况
if(!require(flexclust))(
install.packages("flexclust")
)
clk5 <- cclust(clean_algae_blk[,-c(1:3)], k=5);clk5
barchart(clk5,legend=TRUE)
图.18
###################################################
### Multiple Linear Regression
###################################################
data(algae)
algae <- algae[-manyNAs(algae), ]
clean.algae <- knnImputation(algae, k = 10)
lm.a1 <- lm(a1 ~ .,data=clean.algae[,1:12])
summary(lm.a1)
anova(lm.a1)
lm2.a1 <- update(lm.a1, . ~ . - season)
summary(lm2.a1)
anova(lm.a1,lm2.a1)
final.lm <- step(lm.a1)
summary(final.lm)
#判断共线性问题,小于2，表明变量间共线性弱
vif(final.lm)
###################################################
### Regression Trees
###################################################
library(rpart)
data(algae)
algae <- algae[-manyNAs(algae), ]
rt.a1 <- rpart(a1 ~ .,data=algae[,1:12])
rt.a1
summary(rt.a1)
prettyTree(rt.a1,
compress = T,#布局问题，是否更紧凑
branch = 1, #横线的长短
margin = 0.05, # 图像距离边界的大小
cex = 0.8,#定义字体的大小
fwidth = 0.5,#定义框的宽度
fheight = 0.5,#定义框的高度
center = 0.1)#定义文字在框中的位置
printcp(rt.a1)
rt2.a1 <- prune(rt.a1,cp=0.01) #剪树，cp越大，树越简单
rt2.a1
prettyTree(rt2.a1)
# 生成树的过程剪枝
# set.seed(1234) # Just to ensure same results as in the book
# (rt.xse <- rpartXse(a1 ~ .,data=algae[,1:12]))
# prettyTree(rt.xse)
first.tree <- rpart(a1 ~ .,data=algae[,1:12])
prettyTree(first.tree)
#去掉节点4和7生出的分支,从上到下，从左到右的顺序判断节点的编号
snip.tre <- snip.rpart(first.tree,c(4,7))
prettyTree(snip.tre)
prettyTree(first.tree)
snip.rpart(first.tree)#双击某个节点，则该节点之后的分支就消失了
###################################################
### Model Evaluation and Selection
###################################################
rm(list = ls())
data("algae")
algae <- algae[-manyNAs(algae), ]
clean.algae = knnImputation(algae,k = 10)
lm.a1 <- lm(a1 ~ .,data=clean.algae[,1:12])
final.lm = step(lm.a1)
rt.a1 <- rpart(a1 ~ .,data=algae[,1:12])
lm.predictions.a1 <- predict(final.lm,clean.algae)
rt.predictions.a1 <- predict(rt.a1,algae)
#mae: mean absolute error
(mae.a1.lm <- mean(abs(lm.predictions.a1-algae[,'a1'])))
(mae.a1.rt <- mean(abs(rt.predictions.a1-algae[,'a1'])))
#mse: mean squared error
(mse.a1.lm <- mean((lm.predictions.a1-algae[,'a1'])^2))
(mse.a1.rt <- mean((rt.predictions.a1-algae[,'a1'])^2))
#
(nmse.a1.lm <- mean((lm.predictions.a1-algae[,'a1'])^2)/
mean((mean(algae[,'a1'])-algae[,'a1'])^2))
(nmse.a1.rt <- mean((rt.predictions.a1-algae[,'a1'])^2)/
mean((mean(algae[,'a1'])-algae[,'a1'])^2))
regr.eval(algae[,'a1'],rt.predictions.a1,train.y=algae[,'a1'])
old.par <- par(mfrow=c(1,2))
plot(lm.predictions.a1,algae[,'a1'],main="Linear Model",
xlab="Predictions",ylab="True Values")
abline(0,1,lty=2) #intercept = 0, slope = 1
plot(rt.predictions.a1,algae[,'a1'],main="Regression Tree",
xlab="Predictions",ylab="True Values")
abline(0,1,lty=2)
par(old.par)
plot(lm.predictions.a1,algae[,'a1'],main="Linear Model",
xlab="Predictions",ylab="True Values")
abline(0,1,lty=2)
algae[identify(lm.predictions.a1,algae[,'a1']),]
sensible.lm.predictions.a1 <- ifelse(lm.predictions.a1 < 0,0,lm.predictions.a1)
regr.eval(algae[,'a1'],lm.predictions.a1,stats=c('mae','mse'))
regr.eval(algae[,'a1'],sensible.lm.predictions.a1,stats=c('mae','mse'))
cv.rpart <- function(form,train,test,...) {
m <- rpartXse(form,train,...)
p <- predict(m,test)
mse <- mean((p-resp(form,test))^2)
c(nmse=mse/mean((mean(resp(form,train))-resp(form,test))^2))
}
cv.lm <- function(form,train,test,...) {
m <- lm(form,train,...)
p <- predict(m,test)
p <- ifelse(p < 0,0,p)
mse <- mean((p-resp(form,test))^2)
c(nmse=mse/mean((mean(resp(form,train))-resp(form,test))^2))
}
res <- experimentalComparison(
c(dataset(a1 ~ .,clean.algae[,1:12],'a1')),
c(variants('cv.lm'),
variants('cv.rpart',se=c(0,0.5,1))),
cvSettings(3,10,1234))
summary(res)
plot(res)
getVariant('cv.rpart.v1',res)
DSs <- sapply(names(clean.algae)[12:18],
function(x,names.attrs) {
f <- as.formula(paste(x,"~ ."))
dataset(f,clean.algae[,c(names.attrs,x)],x)
},
names(clean.algae)[1:11])
res.all <- experimentalComparison(
DSs,
c(variants('cv.lm'),
variants('cv.rpart',se=c(0,0.5,1))
),
cvSettings(5,10,1234))
plot(res.all)
bestScores(res.all)
library(randomForest)
cv.rf <- function(form,train,test,...) {
m <- randomForest(form,train,...)
p <- predict(m,test)
mse <- mean((p-resp(form,test))^2)
c(nmse=mse/mean((mean(resp(form,train))-resp(form,test))^2))
}
res.all <- experimentalComparison(
DSs,
c(variants('cv.lm'),
variants('cv.rpart',se=c(0,0.5,1)),
variants('cv.rf',ntree=c(200,500,700))
),
cvSettings(5,10,1234))
bestScores(res.all)
compAnalysis(res.all,against='cv.rf.v3',
datasets=c('a1','a2','a4','a6'))
###################################################
### Predictions for the 7 algae
###################################################
bestModelsNames <- sapply(bestScores(res.all),
function(x) x['nmse','system'])
learners <- c(rf='randomForest',rpart='rpartXse')
funcs <- learners[sapply(strsplit(bestModelsNames,'\\.'),
function(x) x[2])]
parSetts <- lapply(bestModelsNames,
function(x) getVariant(x,res.all)@pars)
bestModels <- list()
for(a in 1:7) {
form <- as.formula(paste(names(clean.algae)[11+a],'~ .'))
bestModels[[a]] <- do.call(funcs[a],
c(list(form,clean.algae[,c(1:11,11+a)]),parSetts[[a]]))
}
clean.test.algae <- knnImputation(test.algae,k=10,distData=algae[,1:11])
preds <- matrix(ncol=7,nrow=140)
for(i in 1:nrow(clean.test.algae))
preds[i,] <- sapply(1:7,
function(x)
predict(bestModels[[x]],clean.test.algae[i,])
)
avg.preds <- apply(algae[,12:18],2,mean)
apply( ((algae.sols-preds)^2),2,mean) / apply( (scale(algae.sols,avg.preds,F)^2),2,mean)
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