title: Not able to merge/join two dataframes by date-time
body: <p>I am trying to join two dataframe by date-time but I have not been successful. I have checked the seconds and they seem to have matches but an inner join return no results. I used <code>merge</code> and <code>tidyverse</code> with the same output. I am including a sample of my actual objects in the script below:</p>
  
  <pre><code>library(tidyverse)
  
  a &lt;- structure(
    list(
      date = structure(c(
        126230400, 126234000, 126237600,
        126241200, 126244800, 126248400, 126252000, 126255600, 126259200,
        126262800, 126266400, 126270000, 126273600, 126277200, 126280800,
        126284400, 126288000, 126291600, 126295200, 126298800, 126302400,
        126306000, 126309600, 126313200
      ), class = c("POSIXct", "POSIXt"), tzone = "UTC"), wd = c(
        303, 317, 309, 312, 274, 298, 311,
        298, 314, 303, 303, 302, 305, 303, 277, 281, 284, 276, 283, 289,
        262, 284, 281, 287
      ), ws = c(
        4.6, 5.2, 4.6, 4.1, 3.1, 4.1, 2.6,
        4.6, 6.2, 2.1, 3.1, 4.6, 4.1, 4.6, 4.6, 5.2, 4.1, 4.1, 4.1, 4.1,
        4.1, 4.6, 3.6, 3.6
      )
    ),
    row.names = c(NA, -24L), class = c(
      "tbl_df",
      "tbl", "data.frame"
    )
  )
  
  b &lt;- structure(
    list(
      date = structure(c(
        126230400, 126234000, 126237600,
        126259200, 126262800, 126266400, 126270000, 126273600, 126277200
      ), class = c("POSIXct", "POSIXt"), tzone = "UTC"), wd = c(
        303,
        321, 292, 291, 309, 296, 282, 285, 288
      ), ws = c(
        3.6525524, 3.85833,
        4.6814404, 4.115552, 4.0126632, 3.4467748, 6.0189948, 5.7103284,
        4.9386624
      )
    ),
    row.names = c(NA, -9L), class = c(
      "tbl_df", "tbl",
      "data.frame"
    )
  )
  
  a %&gt;% inner_join(b)
  </code></pre>