title: Convert data to date, month, year in lubridate in R
body: <p>I have a <code>dataframe</code> with a column with dates, the column is named <code>dateDecision</code>. They are in the format <code>1970/01/01</code>. I am trying to split the date into <code>year</code>, <code>month</code> and <code>date</code> columns. I used the following code</p>
  
  <pre><code>df %&gt;% mutate(year = lubridate::year(dateDecision), 
                  month = lubridate::month(dateDecision), 
                  day = lubridate::day(dateDecision))
  </code></pre>
  
  <p>I get an error saying Error in <code>as.POSIXlt.character(x, tz = tz(x)) : character string is not in a standard unambiguous format</code> </p>
  
  <p>When I use dput(head(df,10)), this is the output</p>
  
  <pre><code>structure(list(term = c("1791", "1791", "1791", "1791", "1791", 
  "1792", "1792", "1792", "1792", "1792"), dateDecision = c("8/3/1791", 
  "8/3/1791", "8/3/1791", "8/3/1791", "8/3/1791", "8/11/1792", 
  "8/11/1792", "8/11/1792", "8/11/1792", "8/11/1792"), decisionType = c("6", 
  "6", "6", "6", "6", "8", "8", "8", "8", "8"), dateArgument = c("8/2/1791", 
  "8/2/1791", "8/2/1791", "8/2/1791", "8/2/1791", "8/9/1792", "8/9/1792", 
  "8/9/1792", "8/9/1792", "8/9/1792")), row.names = c(NA, -10L), class = c("tbl_df", 
  "tbl", "data.frame"))
  </code></pre>
  
  <p>How do I fix this?</p>