R（二）

###################11R的表(求相应组合的频率)######################
age <- c(12, 35, 25, 12, 25)
gender <- c("f", "m", "m", "m", "f")
table(age,gender)
dat<-data.frame(age,gender)
table(dat)
###################12基本运算####################
a<-5
b<-3
a%%b#余数
a%/%b#整除
a/b
c<--5
abs(c)
sign(a)#判断正负
sign(c)
sign(0)
a^b
sqrt(b)
log2(2)
log10(10)
log(4,base = 16)
log(exp(2),exp(1))
isTRUE(TRUE)
isTRUE(FALSE)
identical(1,NULL)#前后是否相等
cumsum(1:5)#累加
cumprod(1:5)#累乘
cumsum(c(1,3,5,7,9))
seq(-3,3)#序列
#unique()找出相异的
a<-c(rep(1,3),rep(2,3),rep(6,7),1:10)
a
#!!重要！！
unique(a)
which(a==6)#下标
#%in%

###################13三角运算####################
sin(1)#1表示弧度
a<-c(1:5)
sin(a)
plot(a,sin(a))
a<-seq(1,10,0.5)
plot(a,sin(a))
plot(a,sin(a),type ='line',col='red' )
cos(1)
plot(a,cos(a),col=rainbow(length(a)))
tan(1)
plot(a,tan(a))
plot(a,tan(a),col=rainbow(length(a)))
asin(1)
atan(2)

###################14解方程####################
#ax+b=0的根(异号)
f<-function(x,a,b){return(a*x+b)}
uniroot(f,c(-10,10),5,10,tol = 0.0001)
root<-uniroot(f,c(-10,10),5,10,tol = 0.0001)
root$root

f2<-function(x,a,b,d){return(a*x^2+b*x+d)}
uniroot(f2,c(-4,-2.55),a=1,b=5,d=6,tol = 0.0011)
root2<-uniroot(f2,c(-4,-2.55),a=1,b=5,d=6,tol = 0.0011)
root2$root
#方程组
f<-matrix(c(3,5,1,2),nrow = 2,byrow = TRUE)
f
rf<-matrix(c(4,1),nrow = 2)
rf
solve(f,rf)

###################15-17for、while、repeat循环####################
a<-c('a','b','c')
#下标访问
for (i in c(1:length(a))) {
  print(i)
}
for (i in c(1:length(a))) {
  print(a[i])
}
#直接访问
for (i in a) {
  print(i)
}
#循环嵌套
a<-matrix(c(1:24),nrow = 4)
a
for (i in c(1:nrow(a)))
  for (j in c(1:ncol(a))) {
    print(a[i,j])
  }
#1到100的和
s<-0
L<-1
while (L<=100) {
  s<-s+L
  L<-L+1
}
s
#e的泰勒级数
e<-1
i<-1
while((1/prod(1:i)-1/prod(1:(i+1)))>0.001){
  print(i)
  e<-e+1/prod(1:i)
  i<-i+1
}
e
#repeat
s<-0
i<-1
repeat{
  if(i>100){
    break()
  }
  s<-s+i
  i<-i+1
}
s

###################18函数基本知识####################
printTest<-function(x){
  print(x)
}
printTest('hello world!')

ret<-function(x,y){
  return(x+y)
}
ret(1,2)
#矩阵相乘函数
mat1<-matrix(c(1:12),nrow = 3,ncol = 4)
mat2<-matrix(c(1:24),nrow = 4,ncol = 6)
f<-function(x,y){
  xcol<-dim(x)[2]
  yrow<-dim(y)[1]
  m<-dim(x)[1]
  n<-dim(y)[2]
  if(xcol!=yrow){
    print('the two matrix diamoids is not equal!')
    return(0)
  }
  mat<-matrix(0,nrow = dim(x)[1],ncol = dim(y)[2])
  for(i in c(1:m))
    for (j in c(1:n)) {
      mat[i,j] <- sum(x[i,]*y[,j])
    }
  return(mat)
}
mat1%*%mat2
f(mat1,mat2)
mat3<-matrix(c(1:14),nrow = 2,ncol = 7)
f(mat1,mat3)

###################19管道函数(%>%,将左边的对象传递给右边函数)####################
#install.packages("dplyr")
library(dplyr)
f<-function(x,y){
  return(x*y)
}
f(2,4)
2%>%f(4)
f2<-function(x,y,z){
  return(x*y+z)
}
f2(2,3,4)
3%>%f2(2,.,4)
#例1
f<-function(x){return(x+1)}
f2<-function(x){return(x^2)}
f3<-function(x){return(sin(x))}
x<-4
x %>% f() %>% f2() %>% f3()
#例2
#install.packages("tidyr")
library(tidyr)
date<-as.Date('2020-04-16')+0:19
date
hour<-sample(1:24,20)
hour
minute<-sample(1:60,20)
minute
second<-sample(1:60,20)
second
dat<-data.frame(date,hour,minute,second)
dat
Sys.time()
dat %>% unite(dateHour,date,hour,sep = ' ') %>% unite(dateHourMinute,dateHour,minute,sep = ':') %>% unite(dateTime,dateHourMinute,second,sep = ':')
dat %>% unite(dateHour,date,hour,sep = ' ') %>% unite(dateTime,dateHour,minute,second,sep = ':')

###################20函数递归####################
fib<-function(n){
  if(n==1||n==2){
    return (1)
  }
  return (fib(n-1)+fib(n-2))
}

for (i in c(1:10)) {
  print(fib(i))
}