title: How can I print tibbles when chunk is run in R Notebook in RStudio?
body: <p>I cannot print a Tibble created by the CSV file below by running a chunk in an R Notebook in RStudio. The following example prints messages about parsing from read_csv but does not print df.  However, when I preview the notebook, the data frame is printed. The data frame is also printed when entering the code using the R console.</p>
  
  <pre><code>---
  title: "Min Example"
  output: html_notebook
  ---
  
  ```{r chunk}
  library(readr)
  library(tibble)
  df &lt;- read_csv('min.csv')
  df
  ```
  </code></pre>
  
  <p>The command head(df) also produces no output when the chunk is run, but summary(df) and str(df) do produce output in the notebook.</p>
  
  <p>I am using the latest version of RStudio, 1.0.136, and my packages are up to date.  My session info follows</p>
  
  <pre><code>R version 3.3.2 (2016-10-31)
  Platform: x86_64-pc-linux-gnu (64-bit)
  Running under: Ubuntu 16.04.1 LTS
  
  locale:
  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8       
  [4] LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                  LC_ADDRESS=C              
  [10] LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] tibble_1.2  readr_1.0.0
  
  loaded via a namespace (and not attached):
  [1] assertthat_0.1 tools_3.3.2    Rcpp_0.12.8    knitr_1.15.1
  </code></pre>
  
  <p>The contents of the CSV file are</p>
  
  <pre><code>ID,Year,PubDate,CWE,CVSS,Vendor,Project
  CVE-1999-0001,1999,1999-12-30,CWE-20,5.0,freebsd,freebsd
  CVE-1999-0002,1998,1998-10-12,CWE-119,10.0,caldera,openlinux
  CVE-1999-0003,1998,1998-04-01,NA,10.0,sgi,irix
  CVE-1999-0004,1997,1997-12-16,NA,5.0,university_of_washington,pine
  CVE-1999-0005,1998,1998-07-20,NA,10.0,university_of_washington,imap
  CVE-1999-0006,1998,1998-07-14,NA,10.0,qualcomm,qpopper
  CVE-1999-0007,1998,1998-06-26,NA,5.0,ssleay,ssleay
  CVE-1999-0008,1998,1998-06-08,NA,10.0,sun,solaris
  CVE-1999-0009,1998,1998-04-08,NA,10.0,sgi,irix
  </code></pre>
  
  <p>Viewing the data frame using dput() produces</p>
  
  <pre><code>structure(list(ID = c("CVE-1999-0001", "CVE-1999-0002", "CVE-1999-0003", 
  "CVE-1999-0004", "CVE-1999-0005", "CVE-1999-0006", "CVE-1999-0007", 
  "CVE-1999-0008", "CVE-1999-0009"), Year = c(1999L, 1998L, 1998L, 
  1997L, 1998L, 1998L, 1998L, 1998L, 1998L), PubDate = structure(c(10955, 
  10511, 10317, 10211, 10427, 10421, 10403, 10385, 10324), class = "Date"), 
      CWE = c("CWE-20", "CWE-119", NA, NA, NA, NA, NA, NA, NA), 
      CVSS = c(5, 10, 10, 5, 10, 10, 5, 10, 10), Vendor = c("freebsd", 
      "caldera", "sgi", "university_of_washington", "university_of_washington", 
      "qualcomm", "ssleay", "sun", "sgi"), Project = c("freebsd", 
      "openlinux", "irix", "pine", "imap", "qpopper", "ssleay", 
      "solaris", "irix")), class = c("tbl_df", "tbl", "data.frame"
  ), row.names = c(NA, -9L), .Names = c("ID", "Year", "PubDate", 
  "CWE", "CVSS", "Vendor", "Project"), spec = structure(list(cols = structure(list(
      ID = structure(list(), class = c("collector_character", "collector"
      )), Year = structure(list(), class = c("collector_integer", 
      "collector")), PubDate = structure(list(format = ""), .Names = "format", class = c("collector_date", 
      "collector")), CWE = structure(list(), class = c("collector_character", 
      "collector")), CVSS = structure(list(), class = c("collector_double", 
      "collector")), Vendor = structure(list(), class = c("collector_character", 
      "collector")), Project = structure(list(), class = c("collector_character", 
      "collector"))), .Names = c("ID", "Year", "PubDate", "CWE", 
  "CVSS", "Vendor", "Project")), default = structure(list(), class = c("collector_guess", 
  "collector"))), .Names = c("cols", "default"), class = "col_spec"))
  </code></pre>
  
  <p>The <a href="http://faculty.cs.nku.edu/~waldenj/diagnostics-report.txt" rel="nofollow noreferrer">RStudio Diagnostics Report</a> is now available.</p>