从xlsx文件加载数据作为日期和时间

Question

Now a xlsx file contained a date column as :

Date
2019-3-1 0:15
2019-3-1 19:15
2019-3-1 23:15

How can I load it into data.frame as read date and time datatype? My tool is openxlsx package and I tried like:

df <- readWorkbook(xlsxFile = '0301-0314.xlsx',sheet=1)

Answer 1

First you read the data set using any library. Then you can try as.POSIXlt or as.POSIXct to define the date-time format. This also allows you to provide timezone info along with date-time format. Example:

> sampledf <- data.frame(DateTime = c("2019-3-1 0:15",
+                            "2019-3-1 19:15",
+                            "2019-3-1 23:15")
+ )
> str(sampledf$DateTime)
 Factor w/ 3 levels "2019-3-1 0:15",..: 1 2 3
> sampledf$DateTime <- as.POSIXlt(sampledf$DateTime ,"GMT",format = "%Y-%m-%d %H:%M")
> str(sampledf$DateTime)
 POSIXlt[1:3], format: "2019-03-01 00:15:00" "2019-03-01 19:15:00" ...

Timezone info "GMT" can be replace with any time zone. More about different time formatting options in R is available here.

Answer 2

This will work:

# Create example dataset:
df <- data.frame(Date = c("2019-3-1 0:15",
                        "2019-3-1 19:15",
                        "2019-3-1 23:15")
                )
df$Date <- as.character(df$Date)
# Format "Date" as date and time:
df$time <- strptime(as.character(df$Date), "%Y-%m-%d %H:%M")
# Check:
str(df)
# If then you would like to count time, for example in number of hours, from a certain initial time (e.g. 2019-3-1 0:15) try:
df$timestep <- as.numeric(difftime(time2="2019-3-1 0:15", time1=df$time, units="hours"))