CW20425

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# Construct a set of vectors contaiing data on three medical patients, 
subject_name <- c("John Doe", "Jane Doe", "Steve Graves")
temperature <- c(98.1, 98.6, 101.4)
flu_status <- c(FALSE, FALSE, TRUE)

# Values stored in R vectors retain their order 
#By index
temperature[2]

## [1] 98.6

#To obtain the body temperature of the second and third patients, type
# By range
temperature[2:3]

## [1]  98.6 101.4

# By exclusion
temperature[-2]

## [1]  98.1 101.4

# Factors are used to represent categorical or ordinal variables

##Coding a factor attribte in R
gender <- factor(c("MALE","FEMALE", "MALE"))
gender

## [1] MALE   FEMALE MALE  
## Levels: FEMALE MALE

#Adding levels ot categorical attributes
blood <- factor(c("O","AB", "A"), levels = c("A", "B", "AB", "O"))
blood

## [1] O  AB A 
## Levels: A B AB O

#Ordinal Factor Attributes, also categorical but includes order
symptoms <- factor(c("SEVERE", "MILD", "MODERATE"), levels = c("MILD", "MODERATE", "SEVERE"), ordered = TRUE)
symptoms

## [1] SEVERE   MILD     MODERATE
## Levels: MILD < MODERATE < SEVERE

#Adding levels to categorical attributes
blood_sign <- factor(c("+", "-"), levels = (c("+", "-")))
blood_sign

## [1] + -
## Levels: + -

symptoms >= "MODERATE"

## [1]  TRUE FALSE  TRUE

# Creating  a data frame
pt_data <- data.frame(subject_name, temperature, flu_status, gender, blood, symptoms, stringsAsFactors = FALSE)
pt_data

##   subject_name temperature flu_status gender blood symptoms
## 1     John Doe        98.1      FALSE   MALE     O   SEVERE
## 2     Jane Doe        98.6      FALSE FEMALE    AB     MILD
## 3 Steve Graves       101.4       TRUE   MALE     A MODERATE

pt_data[1,2]

## [1] 98.1

pt_data[1,]

##   subject_name temperature flu_status gender blood symptoms
## 1     John Doe        98.1      FALSE   MALE     O   SEVERE

#To extract everything
pt_data[,]

##   subject_name temperature flu_status gender blood symptoms
## 1     John Doe        98.1      FALSE   MALE     O   SEVERE
## 2     Jane Doe        98.6      FALSE FEMALE    AB     MILD
## 3 Steve Graves       101.4       TRUE   MALE     A MODERATE

pt_data[c(1,3), c(2,4)]

##   temperature gender
## 1        98.1   MALE
## 3       101.4   MALE

#columns are better accessed by name rather than position
pt_data[c(1,3), c("temperature", "gender")]

##   temperature gender
## 1        98.1   MALE
## 3       101.4   MALE

# Creating new columns in a dataframe
# Convert f
pt_data$temp_c <- (pt_data$temperature - 32)* (5/9)
pt_data$temp_c

## [1] 36.72222 37.00000 38.55556

#Checking if our data is added
pt_data[c("temperature", "temp_c")]

##   temperature   temp_c
## 1        98.1 36.72222
## 2        98.6 37.00000
## 3       101.4 38.55556

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