Subset data by Year from period column - r

Question

I have data with month and year column, how can I subset this to be per year along, here is sample dataset
# Libraries
library(ggplot2)
library(reshape2)
# Data
df <- data.frame("Hospital" = c("Buge Hospital", "Buge Hospital", "Greta Hospital", "Greta Hospital",
"Makor Hospital", "Makor Hospital"),
"Period" = c("Jul-18","Aug-18", "Jul-19","Aug-19", "Jul-20","Aug-20"),
"Medical admissions" = c(12,56,0,40,5,56),
"Surgical admissions" = c(10,2,0,50,20,56),
"Inpatient admissions" = c(9,5,6,0,60,96))
I have tried this but I get empty dataset
data_18 <- subset(df, format(as.Date(df$Period, format="%b/%Y"),"%Y")== 2018)
I want to pull out monthly data for each year so that so that I can observe data trends for that monthly period
Expected result is to subset and get only data for each year individually example is like pull out monthly data for 2018.

Answer 1

I am not sure if this is what you are looking for:
data <- Filter(nrow,split(df,list(gsub(".*-","",df$Period),df$Hospital)))
data_18 <- data[grepl("^18",names(data))]
which gives
> data
$`18.Buge Hospital`
Hospital Period Medical.admissions Surgical.admissions Inpatient.admissions
1 Buge Hospital Jul-18 12 10 9
2 Buge Hospital Aug-18 56 2 5
$`19.Greta Hospital`
Hospital Period Medical.admissions Surgical.admissions Inpatient.admissions
3 Greta Hospital Jul-19 0 0 6
4 Greta Hospital Aug-19 40 50 0
$`20.Makor Hospital`
Hospital Period Medical.admissions Surgical.admissions Inpatient.admissions
5 Makor Hospital Jul-20 5 20 60
6 Makor Hospital Aug-20 56 56 96
and
> data_18
$`18.Buge Hospital`
Hospital Period Medical.admissions Surgical.admissions Inpatient.admissions
1 Buge Hospital Jul-18 12 10 9
2 Buge Hospital Aug-18 56 2
EDIT
If you just want to subset data in 2018 (thanks to #G. Grothendieck )
data_18 <- subset(df, grepl("18", Period))

Answer 2

I think what you were trying for is :
subset(df, format(as.Date(paste('1', Period), '%d %b-%y'), "%Y") == 2018)
# Hospital Period Medical.admissions Surgical.admissions Inpatient.admissions
#1 Buge Hospital Jul-18 12 10 9
#2 Buge Hospital Aug-18 56 2 5
Or using zoo's yearmon.
library(zoo)
subset(df, floor(as.yearmon(Period, "%b-%y")) == 2018)

Answer 3

There are several possibilities, for example with strsplit or with tidyverse as follows:
library(tidyr)
library(dplyr)
df %>% separate(Period, into=c("Month", "Year"), "-") %>% filter(Year == 18)
and if you want to summarize, plot or something, use group_by instead of filter, for example:
df %>%
separate(Period, into=c("Month", "Year"), "-") %>%
group_by(Year) %>%
summarize(sum(Medical.admissions))

Answer 4

And for a more pedestrian approach in response to your desire to subset on both year and month, and to reflect how the approach in your own code could be made to work:
# Libraries
library(ggplot2)
library(reshape2)
library(lubridate)
# Data
df <- data.frame("Hospital" = c("Buge Hospital", "Buge Hospital", "Greta Hospital", "Greta Hospital",
"Makor Hospital", "Makor Hospital"),
"Period" = c("Jul-18","Aug-18", "Jul-19","Aug-19", "Jul-20","Aug-20"),
"Medical admissions" = c(12,56,0,40,5,56),
"Surgical admissions" = c(10,2,0,50,20,56),
"Inpatient admissions" = c(9,5,6,0,60,96),
stringsAsFactors = FALSE)
# data wrangle to give you a valid date and year varibles, subsetting on year should be straightforward using dplyr::group_by(year, month)
df1 <-
df %>%
mutate(date = as.Date(paste0("01-", Period),format = "%d-%b-%y"),
year = year(date),
month = month(date))