Join two numeric columns to create a Year-month variable

Question

I have two numeric columns. One contains a year, one a month number. I want to join these two and make a Year-month column that is of the proper Date type. To give a background, the reason I can't keep it as a character type is that I am plotting these points. They don't sort properly if they are char. For example, instead of

2015 1
2015 2
...
2015 12

We would see the sort order as

2015 1
2015 10
2015 11
2015 12
...

So if there is some kind of character hack that works the same as a conversion to a Date type, that will work too.

Sorry for this relatively simple question. I am ok with R but struggle with formatting.

Sample code for re-creating

month<-as.character(seq(1,12,1))
year<-'2015'

df<-data.frame(paste(year,month))

Answer 1

In order to be a proper date type, you need a month, day, and year. I usually just throw a "1" in there for the day, since every month has a first day...

df <- data.frame(year=c("2015", "2015", "2014"),
                 month=c("4", "2", "9"),
                 stringsAsFactors=FALSE)
df$date <- as.Date(paste(df$month, "01", df$year, sep="_"), format="%m_%d_%Y")
df <- df[order(df$date), ]

Answer 2

您可以考虑在Zoo软件包中使用yearmon类：

library(zoo) zoo::as.yearmon(paste(year, month, sep='-'))

Answer 3

只需在粘贴中添加01并使用as.Date

as.Date(paste(year, month, '01', sep= '-'))