Demo20220316

##Matrix

kevin <- c(85,73)
marry <- c(72,64)
jerry <- c(59,66)

mat <- matrix(c(kevin, marry, jerry), nrow = 3, byrow = TRUE)

#?matrix

kevin[1]

## [1] 85

mat[1,1]

## [1] 85

# method 1
mat[ , 1 ] * 0.4 + mat[ , 2] * 0.6

## [1] 77.8 67.2 63.2

# method 2
mat %*% c(0.4,0.6)

##      [,1]
## [1,] 77.8
## [2,] 67.2
## [3,] 63.2

Factor

weather <- c('sunny', 'rainy', 'cloudy', 'rainy', 'cloudy')

class(weather)

## [1] "character"

weather_category <- factor(weather)
class(weather_category)

## [1] "factor"

temperature  <- c('Low', 'High', 'High', 'Medium', 'Low', 'Medium')

class(temperature)

## [1] "character"

factor(temperature)

## [1] Low    High   High   Medium Low    Medium
## Levels: High Low Medium

temperature_category <- factor(temperature, order = TRUE, levels = c('Low', 'Medium', 'High'))

temperature_category[3]

## [1] High
## Levels: Low < Medium < High

temperature_category[1]

## [1] Low
## Levels: Low < Medium < High

temperature_category[3] > temperature_category[1]

## [1] TRUE

temperature_category[4]

## [1] Medium
## Levels: Low < Medium < High

temperature_category[4] > temperature_category[3]

## [1] FALSE

levels(temperature_category)

## [1] "Low"    "Medium" "High"