bday

library(tidyr)
library(ggplot2)
library(ggthemes)
library(dplyr)

## 
## Attaching package: 'dplyr'
## 
## The following object is masked from 'package:stats':
## 
##     filter
## 
## The following objects are masked from 'package:base':
## 
##     intersect, setdiff, setequal, union

tmp = read.csv('birthdaysExample.csv')
head(tmp)

##      dates
## 1 11/25/14
## 2   6/8/14
## 3  9/12/14
## 4  5/26/14
## 5  2/20/14
## 6  6/19/14

tmp$dates = as.Date(tmp$dates, "%m/%d/%y")
head(tmp)

##        dates
## 1 2014-11-25
## 2 2014-06-08
## 3 2014-09-12
## 4 2014-05-26
## 5 2014-02-20
## 6 2014-06-19

str(tmp)

## 'data.frame':    1033 obs. of  1 variable:
##  $ dates: Date, format: "2014-11-25" "2014-06-08" ...

Amount of people who share the same b-day with me:

length(filter(tmp, dates=='2014-07-31')$dates)

## [1] 3

Which month contains the most number of birthdays?

March has 98 birthdays which is the highest compare to other months:

tmp$month = format(tmp$dates, "%m")
head(tmp)

##        dates month
## 1 2014-11-25    11
## 2 2014-06-08    06
## 3 2014-09-12    09
## 4 2014-05-26    05
## 5 2014-02-20    02
## 6 2014-06-19    06

countByMonth = tmp %>%
  group_by(month) %>%
  summarise(n = n())
head(countByMonth)

## Source: local data frame [6 x 2]
## 
##   month  n
## 1    01 89
## 2    02 79
## 3    03 98
## 4    04 81
## 5    05 72
## 6    06 93

max(names(table(countByMonth$n)))

## [1] "98"

How many birthdays are in each month?

countByMonth

## Source: local data frame [12 x 2]
## 
##    month  n
## 1     01 89
## 2     02 79
## 3     03 98
## 4     04 81
## 5     05 72
## 6     06 93
## 7     07 86
## 8     08 91
## 9     09 96
## 10    10 89
## 11    11 87
## 12    12 72

Which day of the year has the most number of birthdays?

max(table(tmp$dates))

## [1] 8

t = table(tmp$dates)
d = as.data.frame(t)
filter(d, Freq==8)

##         Var1 Freq
## 1 2014-02-06    8
## 2 2014-05-22    8
## 3 2014-07-16    8

2014-02-06, 2014-05-22 and 2014-07-16 have the most number of birthdays.

tmp$day = format(tmp$dates, "%d")
head(tmp)

##        dates month day
## 1 2014-11-25    11  25
## 2 2014-06-08    06  08
## 3 2014-09-12    09  12
## 4 2014-05-26    05  26
## 5 2014-02-20    02  20
## 6 2014-06-19    06  19

By accumulating the birth for each day of every month, the 14th has the most number of birthday.

Do you have at least 365 friends that have birthdays on everyday of the year?

I print out the unique number of days within each month:

tmp$month_num = as.numeric(tmp$month)

vector = numeric(12)

for (i in 1:12){
  vector[i] = length(unique((tmp[tmp$month_num==i,])$day))
}
vector

##  [1] 31 25 30 28 29 29 31 28 30 31 28 28

We can see that only Jan, July, Sep and Oct have enough birthdays to fill the entire month.