Hw4

dta <- read.table("/Users/Tjlee/Desktop/weather/usBirths2015.txt", header = T)
dta

##     birth     month
## 1  325955   January
## 2  298058  February
## 3  328923     March
## 4  320832     April
## 5  327917       May
## 6  330541      June
## 7  353415      July
## 8  351791    August
## 9  347516 September
## 10 339007   October
## 11 318820  November
## 12 335722  December

str(dta)

## 'data.frame':    12 obs. of  2 variables:
##  $ birth: int  325955 298058 328923 320832 327917 330541 353415 351791 347516 339007 ...
##  $ month: Factor w/ 12 levels "April","August",..: 5 4 8 1 9 7 6 2 12 11 ...

dta$month <- c("spring", "spring", "spring", "summer", "summer", "summer", "fall", "fall", "fall", "winter", "winter", "winter")
dta

##     birth  month
## 1  325955 spring
## 2  298058 spring
## 3  328923 spring
## 4  320832 summer
## 5  327917 summer
## 6  330541 summer
## 7  353415   fall
## 8  351791   fall
## 9  347516   fall
## 10 339007 winter
## 11 318820 winter
## 12 335722 winter

season <- aggregate(birth ~ month, sum, data=dta)
season

##    month   birth
## 1   fall 1052722
## 2 spring  952936
## 3 summer  979290
## 4 winter  993549