	Platforms	Pros	Cons
Atom	Cross	built-in markdown file preview
Brackets	Cross	good for web designer
Emacs	Cross	split the buffers
Gedit	Cross	print preview (incorrect when landscape but pdf is right)	no code folding
Geany	Cross	print preview; Terminal; split window
IntelliJ IDEA	Cross
Notepad++	Win	print line numbers, Right-click menu	R syntax highlight not work with most themes
Qt Creator	Cross	split a window (even same file)
RStudio	Cross	folding, best IDE for R coding	not support drag and drop a file but SendTo works
Sublime	Cross
vi	Cross
Visual Studio Code	Cross	Integrated Terminal, Markdown preview	Should not include minimap function

HTML editors: see here.

Atom

Markdown preview feature is OK but it cannot export to pdf or HTML.
pandoc conversion to html/PDF is not good; scripts part has no rectangle, tables have no separate lines.

Packages

To install a new package, go to Preferences -> Install -> type the package name and hit ENTER.

To remove a package, just delete the related folder.

rm -rf ~/.atom/packages/markdown-toc

Markdown Preview Enhanced. It allows to view in browser (html) or export to PDF. Use r instead of R for R language syntax highlight. Another nice feature is the scrollings of the markdown file and preview are together.
Markdown TOC. It messes up the # sign in script blocks :( So I switch to RStudio which has a good support to create the TOC (YAML header).

Install it from the Snap Store on Linux