Changing month name and year to date or POSIXct

Question

I have a data frame

             date     df discharge cfs   green discharge cfs   north discharge cfs
1   December 2018        2520.1394           171.69667             


        

Answer 1

In base R, we can paste an arbitrary date , convert to date object and then format

format(as.Date(paste0('1', df$date), '%d %B %Y'), '%m-%Y')

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Another option with regex and using an inbuilt vector month.name can be

with(df, paste(match(sub('\\s\\d+', '', date), month.name), 
                     sub('.*\\s+', '', df$date), sep = '-'))

Answer 2

We can use as.yearmon to convert to yearmon class and then change the format

library(zoo)
df1$date <- format(as.yearmon(df1$date, "%B %Y"), "%m-%Y")
df1$date
#[1] "12-2018" "11-2018" "10-2018" "04-2019" "08-2019" "02-2019" "01-2019" "07-2019" "06-2019" "03-2019" "05-2019" "11-2019" "10-2019"
#[14] "09-2019"

data

df1 <- structure(list(date = c("December 2018", "November 2018", "October 2018", 
"April 2019", "August 2019", "February 2019", "January 2019", 
"July 2019", "June 2019", "March 2019", "May 2019", "November 2019", 
"October 2019", "September 2019"), df_discharge_cfs = c(2520.1394, 
3475.1023, 1863.4778, 3244.5356, 335.5074, 1631.3048, 1767.6266, 
496.9439, 1097.2101, 1081.8046, 1507.8582, 2842.3542, 544.3002, 
295.72), green_discharge_cfs = c(171.69667, 239.00738, 121.9172, 
260.38507, 14.95659, 94.35956, 132.69408, 26.37159, 64.17292, 
80.32419, 100.81569, 284.72917, 34.67999, 11.37943), 
north_discharge_cfs = c(338.81082, 
422.19063, 200.94455, 543.34792, 29.29938, 198.19885, 247.54493, 
57.50114, 143.40153, 167.57954, 236.58269, 586.75, 83.58193, 
26.25823)), class = "data.frame", row.names = c("1", "2", "3", 
"4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14"))