I have a column with dates as character in the format `10/17/2017 12:00:00 AM`. I want parse the string and keep only the date part as class `Date`, i.e. `2017-10-17`. I am using -

```
df$ReportDate = as.Date(df$ReportDate, format = "%m/%d/%Y %I:%M:%S %p") 
df$ReportDate = as.Date(format(df$ReportDate, "%Y-%m-%d"))

```

this works, but the dataframe has over 5 million rows so this takes close to two mins.

```
  user  system elapsed 
104.73    0.55  105.46 

```

Is there a faster and more efficient way to do this?