title: How to merge using POSIXct variable
body: <p>I am attempting to merge two dataframes by a POSIXct column. I am using tidyverse and lubridate. <em>inner_join()</em> returns an empty dataframe while <em>full_join()</em> returns duplicates for the shorter fram. Is this a bug or is there a more appropriate or preferred method for joining by POSIX objects?</p>
  
  <pre><code>&gt; library(tidyverse)
  &gt; library(lubridate)
  
  &gt; d1 &lt;- tibble(date = as.POSIXct(seq(Sys.time() - days(1), Sys.time(), by = "min"), tz = "America/New_York"))
  &gt; head(d1)
  # A tibble: 6 x 1
    date               
    &lt;dttm&gt;             
  1 2018-03-09 14:01:34
  2 2018-03-09 14:02:34
  3 2018-03-09 14:03:34
  4 2018-03-09 14:04:34
  5 2018-03-09 14:05:34
  6 2018-03-09 14:06:34
  
  &gt; d2 &lt;- tibble(date = as.POSIXct(seq(Sys.time() - days(2), Sys.time(), by = "min"), tz = "America/New_York"))
  &gt; head(d2)
  # A tibble: 6 x 1
    date               
    &lt;dttm&gt;             
  1 2018-03-08 14:01:55
  2 2018-03-08 14:02:55
  3 2018-03-08 14:03:55
  4 2018-03-08 14:04:55
  5 2018-03-08 14:05:55
  6 2018-03-08 14:06:55
  
  &gt; data &lt;- inner_join(d1, d2, by = "date")
  &gt; head(data)
  # A tibble: 0 x 1
  # ... with 1 variable: date &lt;dttm&gt;
  
  &gt; data &lt;- inner_join(d1, d2, by = "date")
  &gt; head(data)
  # A tibble: 0 x 1
  # ... with 1 variable: date &lt;dttm&gt;
  
  &gt; data &lt;- merge(d1, d2, by = "date")
  &gt; dim(data)
  [1] 0 1
  
  &gt; sessionInfo()
  R version 3.4.2 (2017-09-28)
  Platform: x86_64-apple-darwin15.6.0 (64-bit)
  Running under: macOS High Sierra 10.13.3
  
  Matrix products: default
  BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
  LAPACK: /Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRlapack.dylib
  
  locale:
  [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
   [1] lubridate_1.7.3 forcats_0.3.0   stringr_1.3.0   dplyr_0.7.4     purrr_0.2.4     readr_1.1.1     tidyr_0.8.0    
   [8] tibble_1.4.2    ggplot2_2.2.1   tidyverse_1.2.1
  
  loaded via a namespace (and not attached):
   [1] Rcpp_0.12.15     cellranger_1.1.0 pillar_1.2.1     compiler_3.4.2   plyr_1.8.4       bindr_0.1       
   [7] tools_3.4.2      jsonlite_1.5     nlme_3.1-131.1   gtable_0.2.0     lattice_0.20-35  pkgconfig_2.0.1 
  [13] rlang_0.2.0      psych_1.7.8      cli_1.0.0        rstudioapi_0.7   yaml_2.1.18      parallel_3.4.2  
  [19] haven_1.1.1      bindrcpp_0.2     xml2_1.2.0       httr_1.3.1       hms_0.4.1        grid_3.4.2      
  [25] glue_1.2.0       R6_2.2.2         readxl_1.0.0     foreign_0.8-69   modelr_0.1.1     reshape2_1.4.3  
  [31] magrittr_1.5     scales_0.5.0     rvest_0.3.2      assertthat_0.2.0 mnormt_1.5-5     colorspace_1.3-2
  [37] stringi_1.1.6    lazyeval_0.2.1   munsell_0.4.3    broom_0.4.3      crayon_1.3.4
  </code></pre>