R: Group data frame by time intervals
<p>I have a following data frame of customer transactions:</p>

<pre><code>CustID    TransID    Product    Datetime
1         1A         Milk       19:13.7
1         1A         Bread      19:13.7
2         2A         Butter     20:15.1
2         2A         Soda       20:15.1
</code></pre>

<p>I am reading the file as:</p>

<pre><code>df = read.csv("data.csv", as.is = TRUE)
</code></pre>

<p>In that case, the <code>typeof(df$Datetime)</code> is <code>character</code>.</p>

<p>How do I create three groups from this data frame to reflect transaction in Morning, Afternoon and Evening?</p>

<p>Basically I am looking to create three data frames:
    dfMorning
    dfAfternoon
    dfEvening</p>