R Markdown:knitr选项results='hide'不起作用

我试图生成一个执行并显示代码但隐藏输出的块代码。我知道这样做的方法是 echo = T, results = 'hide' 在里面 knitr here . 然而,在我的情况下,这仍然产生输出,有什么想法为什么?

我的会话信息:

> sessionInfo()
R version 3.4.3 (2017-11-30)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

Matrix products: default

locale:
[1] LC_COLLATE=English_United Kingdom.1252 
[2] LC_CTYPE=English_United Kingdom.1252   
[3] LC_MONETARY=English_United Kingdom.1252
[4] LC_NUMERIC=C                           
[5] LC_TIME=English_United Kingdom.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] compiler_3.4.3  backports_1.1.2 rprojroot_1.3-2 htmltools_0.3.6
 [5] tools_3.4.3     yaml_2.2.0      Rcpp_0.12.19    rmarkdown_1.10 
 [9] knitr_1.20      digest_0.6.18   evaluate_0.12