data_management.r

# reading data into R: http://goo.gl/bAUmj

library("ISwR")

#factors

pain <- c(0,3,2,2,1)
fpain <- factor(pain,levels=0:3)
levels(fpain) <- c("none","mild","medium","severe")
fpain

# lists
intake.pre <- c(5260,5470,5640,6180,6390,6515,6805,7515,7515,8230,8770)
intake.post <- c(3910,4220,3885,5160,5645,4680,5265,5975,6790,6900,7335)
mylist <- list(before=intake.pre,after=intake.post)
mylist
mylist$before

# data frames

d <- data.frame(intake.pre,intake.post) 
d
d$intake.pre


# indexing
intake.pre[5]
intake.pre[c(3,5,7)]
v <- c(3,5,7)
intake.pre[v]
intake.pre[1:5]
intake.pre[-c(3,5,7)]
intake.post[intake.pre > 7000]
intake.post[intake.pre > 7000 & intake.pre <= 8000]
intake.pre > 7000 & intake.pre <= 8000

# indexing and dataframes
d <- data.frame(intake.pre,intake.post)
d[5,1]
d[5,]
d[d$intake.pre>7000,]
sel <- d$intake.pre>7000
sel
d[sel,]
d[1:2,]
head(d)


#grouped data and dataframes
energy
exp.lean <- energy$expend[energy$stature=="lean"]
exp.obese <- energy$expend[energy$stature=="obese"]
l <- split(energy$expend, energy$stature)
l

# recoding
age <- subset(juul, age >= 10 & age <= 16)$age
range(age)
agegr <- cut(age, seq(10,16,2), right=F, include.lowest=T)
agegr
length(age)
table(agegr)
q <- quantile(age, c(0, .25, .50, .75, 1)) 
q
ageQ <- cut(age, q, include.lowest=T)
table(ageQ)
levels(ageQ) <- c("1st", "2nd", "3rd", "4th")
levels(agegr) <- c("10-11", "12-13", "14-15")
table(ageQ)
table(agegr)

# manipulating factor levels
pain <- c(0,3,2,2,1)
fpain <- factor(pain,levels=0:3,
        labels=c("none","mild","medium","severe"))
text.pain <-  c("none","severe", "medium", "medium", "mild")
factor(text.pain)
ftpain <- factor(text.pain)
ftpain
ftpain2 <- factor(ftpain, levels=c("none", "mild", "medium", "severe"))
ftpain2


# dates
stroke <- read.csv2(system.file("rawdata","stroke.csv", package="ISwR"), na.strings=".")
names(stroke)
names(stroke) <- tolower(names(stroke))
names(stroke)
head(stroke)
stroke <- transform(stroke,
   died = as.Date(died, format="%d.%m.%Y"),
   dstr = as.Date(dstr, format="%d.%m.%Y"))
summary(stroke$died)
summary(stroke$dstr)
summary(stroke$died - stroke$dstr)
head(stroke$died - stroke$dstr)
stroke <- transform(stroke,
  end = pmin(died,  as.Date("1996-1-1"), na.rm = T),
  dead = !is.na(died) & died < as.Date("1996-1-1"))
head(stroke)
stroke <- transform(stroke,
  obstime = as.numeric(end - dstr, units="days")/365.25)
head(stroke)






# data merge and data frame restructuring
juulgrl <- subset(juul, sex==2, select=-c(testvol,sex))
head(juulgrl)
juulboy <- subset(juul, sex==1, select=-c(menarche,sex))
head(jullboy)
juulgrl$sex <- factor("F")
juulgrl$testvol <- NA
juulboy$sex <- factor("M")
juulboy$menarche <- NA
juulall <- rbind(juulboy, juulgrl)
names(juulall)
levels(juulall$sex)


#sqldf
# Load the package
# install.packages("sqldf")
# install.packages("PASWR")
library(sqldf)
# Use the titanic data set

data(titanic3, package="PASWR")
colnames(titanic3)
head(titanic3)
sqldf('select age, count(*) from titanic3 where age is not null group by age')
library(ggplot2)

DF=sqldf('select age from titanic3 where age != "NA"')
qplot(DF$age,data=DF, geom="histogram")
DF=sqldf('select count(*) total from titanic3 where age=29 group by survived')
DF2=t(DF)

colnames(DF2)=c('Died','Survived')
head(DF2)


# character data

x = 7
y = 10
cat('x should be greater than y, but x=',x,'and y=',y,'\n')
cat('Long strings can','be displayed over',
    'several lines using','the fill= argument',
    fill=40)
paste('one',2,'three',4,'five')
paste(c('one','two','three','four'))
paste(c('one','two','three','four'),collapse=' ')
paste('X',1:5,sep='')
paste(c('X','Y'),1:5,sep='')
paste(c('X','Y'),1:5,sep='_',collapse='|')
paste(c('X','Y'),1:5,'^',c('a','b'),sep='_',collapse='|')
paste(c('X','Y'),1:5,'^',c('a','b'),sep='_')

head(state.name)
substring(state.name,2,6)
mystring = 'dog cat duck'
substring(mystring,c(1,5,9),c(3,7,12))

state = 'Mississippi'
ll = nchar(state)
ll
ltrs = substring(state,1:ll,1:ll)
ltrs
which(ltrs == 's')

# loops and repeats

for (i in 1:5) print(i^2)
j<-k<-0

for (i in 1:5) { 
  j<- j+1 
  k<-k+i*j 
  print(i+j+k) 
}

fac2<-function(x) { f <- 1
    t <- x
    while(t>1) {
        f <- f*t
        t <- t-1 
        } 
        return(f) 
      }
sapply(0:5,fac2)


fac3 <- function(x) { 
  f <- 1
  t <- x
  repeat {
      if (t<2) break 
      f <- f*t 
      t <- t-1 } 
      return(f) }
sapply(0:5,fac3)


cumprod(1:5)

fac4<-function(x) max(cumprod(1:x))
sapply(0:5,fac4)


fibonacci<-function(n) { 
  a<-1
  b<-0 
  while(n>0)
  {swap<-a 
    a<-a+b 
    b<-swap 
    n<-n-1 }
    b}
sapply(1:10,fibonacci)

# avoiding loops
for (i in 1:length(y)) { if(y[i] < 0) y[i] <- 0 }
y [y < 0] <- 0