title: knitr's eval = FALSE not working in R Notebook (still runs code)
body: <p>From all the sources I know (<a href="https://yihui.name/knitr/options/?version=1.1.50&amp;mode=desktop" rel="noreferrer">here</a> and <a href="http://r4ds.had.co.nz/r-markdown.html#" rel="noreferrer">here</a>, for instance), the chunk option <code>eval = FALSE</code> in R is supposed to stop the code from running and only display the code in a knitted document. However, the chunks marked with <code>eval = FALSE</code> in my Rstudio always run. </p>
  
  <p>I am not what is the best way to display this issue, so I attached a screenshot below:</p>
  
  <p><a href="https://i.stack.imgur.com/gMtMI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/gMtMI.png" alt="enter image description here"></a></p>
  
  <p>the command <code>plot(cars)</code> always get evaluated despite the selected option. While <code>include = FALSE</code> can prevent the graph from showing the Console suggests that the code was still executed for the multiple times I run the R document.</p>
  
  <pre><code>&gt; plot(cars)
  &gt; plot(cars)
  &gt; plot(cars)
  &gt; plot(cars)
  &gt; plot(cars)
  &gt; 
  </code></pre>
  
  <p><strong>Question</strong></p>
  
  <p>I have searched for a while but did not see other people have similar issues yet, and was wondering how to prevent the <code>echo=FALSE</code> code chunks from running.</p>
  
  <p><strong>Session Info</strong></p>
  
  <pre><code>&gt; sessionInfo()
  R version 3.3.1 (2016-06-21)
  Platform: x86_64-apple-darwin13.4.0 (64-bit)
  Running under: OS X 10.12.3 (Sierra)
  
  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] qwraps_0.2.2      reshape2_1.4.2    devtools_1.12.0   gridExtra_2.2.1   astsa_1.7        
   [6] pander_0.6.0      vars_1.5-2        lmtest_0.9-35     strucchange_1.5-1 sandwich_2.3-4   
  [11] MASS_7.3-45       forecast_7.3      timeDate_3012.100 zoo_1.7-14        urca_1.3-0       
  [16] tsDyn_0.9-44      tseries_0.10-37   stringr_1.1.0     lubridate_1.6.0   forcats_0.2.0    
  [21] dplyr_0.5.0       purrr_0.2.2       readr_1.0.0       tidyr_0.6.1       tibble_1.2       
  [26] ggplot2_2.2.1     tidyverse_1.1.1  
  
  loaded via a namespace (and not attached):
   [1] httr_1.2.1          jsonlite_1.2        foreach_1.4.3       modelr_0.1.0        assertthat_0.1     
   [6] highr_0.6           yaml_2.1.14         backports_1.0.5     lattice_0.20-34     quadprog_1.5-5     
  [11] digest_0.6.12       rvest_0.3.2         colorspace_1.3-2    htmltools_0.3.5     Matrix_1.2-8       
  [16] plyr_1.8.4          psych_1.6.12        broom_0.4.2         haven_1.0.0         bookdown_0.3       
  [21] scales_0.4.1        git2r_0.18.0        mgcv_1.8-17         tseriesChaos_0.1-13 withr_1.0.2        
  [26] nnet_7.3-12         lazyeval_0.2.0      mnormt_1.5-5        magrittr_1.5        readxl_0.1.1       
  [31] memoise_1.0.0       evaluate_0.10       nlme_3.1-131        xml2_1.1.1          foreign_0.8-67     
  [36] rsconnect_0.7       tools_3.3.1         hms_0.3             munsell_0.4.3       grid_3.3.1         
  [41] iterators_1.0.8     htmlwidgets_0.8     base64enc_0.1-3     labeling_0.3        rmarkdown_1.3      
  [46] gtable_0.2.0        codetools_0.2-15    fracdiff_1.4-2      curl_2.3            DBI_0.5-1          
  [51] R6_2.2.0            knitr_1.15.1        rprojroot_1.2       stringi_1.1.2       parallel_3.3.1     
  [56] Rcpp_0.12.9        
  </code></pre>