As explained on this site it is possible to define parameters in the YAML header of a Rmarkdown file and the default values specified there can be overwritten with rmarkdown::render("foo.Rmd", params = list(param1 = "bar"). However when I try this I get the following error:
params object already exists in knit environment so can't be overwritten by render params
Here is a minimal reproducible Rmd document. Let's say the file name is test.Rmd.
---
title: "Test"
output: pdf_document
params:
name: Andreas
---
Hello, my name is `r params$name`.
When I now try rmarkdown::render("test.Rmd", params = list(name = "Jordan") it stops with the error written above.
This is my sessionInfo():
R version 3.2.1 (2015-06-18)
Platform: x86_64-apple-darwin14.4.0 (64-bit)
Running under: OS X 10.10.4 (Yosemite)
locale:
[1] de_DE.UTF-8/de_DE.UTF-8/de_DE.UTF-8/C/de_DE.UTF-8/de_DE.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] knitr_1.11 rmarkdown_0.7.3
loaded via a namespace (and not attached):
[1] Rcpp_0.12.0 XML_3.98-1.3 digest_0.6.8 MASS_7.3-40 grid_3.2.1
[6] plyr_1.8.3 gtable_0.1.2 magrittr_1.5 scales_0.2.5 ggplot2_1.0.1
[11] stringi_0.5-5 reshape2_1.4.1 jwiDlst_0.1.1 proto_0.3-10 tools_3.2.1
[16] stringr_1.0.0 munsell_0.4.2 yaml_2.1.13 parallel_3.2.1 colorspace_1.2-6
[21] htmltools_0.2.6
Thanks for you help!
The error message indicates you have already got an object named params in your current workspace, and you should remove it (rm(params)) before calling rmarkdown::render(). Use ls() to double check the objects in the current environment.
Alternatively - knit the document in a new environment by including the option envir = new.env():
rmarkdown::render("test.Rmd", params = list(name = "Jordan"), envir = new.env() )
I like to do this in any case to make sure the rmarkdown report only uses objects that were explicitly defined as part of its own code.
来源：https://stackoverflow.com/questions/32024013/cant-change-params-in-rmd-documents