How can I draw flowchart-graph example in tikz?

Question

Here I am using https://mermaid.live/ to create a flowcharts. For example with the following code:

flowchart TB
   subgraph w1
       A
       B
       C
   end
   subgraph w2
       D
       E
   end
   subgraph w3
       F
   end
   A & B & C --> D & E
   D & E --> F

It generates:

---

Looks like mermaid handles subgraphs as an array and generates boxes side by side.

It it possible to generate this example flowchart in tikz? if possible dynamically, where new nodes could be added in each subgraph like:

<A B C D E ...>
  <F G H ...>
  <Y Z ...>

The closest I was able to come up with is as follows, with the help from https://tex.stackexchange.com/a/357573/127048 :

\documentclass[tikz,border=2pt]{standalone}
\usepackage{tikz, tikzscale}
\usepackage{paralist} % compactitem
\usetikzlibrary{
    shapes.geometric,
    arrows,
    arrows.meta,
    calc,
    positioning,
    decorations.pathreplacing,
    calligraphy, % had to be after lib. decorations.pathreplacing
    bending} % add geometric shapes and arrows for flowcharts, plus calc package, positioning for relative positions
\tikzstyle{startstop} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm, text centered, draw=black, fill=white]
\tikzstyle{process} = [rectangle, minimum width=3cm, minimum height=1cm, text centered, draw=black, fill=white]
\tikzstyle{process2} = [rectangle, minimum width=3cm, minimum height=1cm, text centered, draw=black, fill=white]
\tikzstyle{process3} = [rectangle, minimum width=3cm, minimum height=1cm, text centered, draw=black, fill=white]
\tikzstyle{arrow} = [thick,->,>=stealth]
\begin{document}
\begin{tikzpicture}[
transform shape,
node distance = 22mm and 11mm,
   box/.style = {shape=rectangle, draw, thin,
                 minimum height=10mm, text width=32mm, align=center,
                 top color=#1!20, bottom color=#1!80,
                 anchor=south west
                 },
BC/.style args = {#1/#2/#3}{ % Braces Calligraphic
        decorate,
        decoration={calligraphic brace, amplitude=6pt,
        raise=#1,
              #2, % for mirroring of brace
        aspect=#3},
        very thick
        },
]
\node (start) [process, align=center] {A};
\node (pro1) [process, right of=start, align=center, xshift=2cm] {B};
\node (pro2) [process, right of=pro1, align=center, xshift=2cm] {C};
\node (pro3) [process2, below of=start, align=center, yshift=-.5cm] {D};
\node (pro4) [process2, below of=pro2, yshift=-.5cm] {E};
\node (main) [startstop, below of=pro1, yshift= -2cm, fill=black!30] {F};
\draw[-Stealth] (start) edge (pro3)
                (start) edge (pro4)
                (pro1) edge (pro3)
                (pro1) edge (pro4)
                (pro2) edge (pro3)
                (pro2) edge (pro4)
                (pro3) edge (main)
                (pro4) edge (main)
\end{tikzpicture}
\end{document}

output:

Answer 1

The most automatic approach without implementing something new is in my opinion a combination of the graphs library and the graphdrawing library (need Lua) with its layered sublibrary.

The name / text[options] // … syntax describes a sublayout with the name name and its text text. Unfortunately, the implementation of the text label is somewhat bare which is why I've used subgraph text none (i.e. w1, w2 and w3 won't show up anywhere) and using an good old label for giving the sublayout a, well, label.

It appears as if the sublayouts are added very late which means they will cover any containing nodes and edges. This is why I give them each a proper name I can access at the end of the picture.

While there might be away to hack the node operation to be put on a different layer than the current for this simple example I'd go with the tried and tested approach.

---

For a more automatic approach take a look at \tikzsimpleflowchart:

\tikzsimpleflowchart{{A, B, C, D, E}, {F, G, H}, {I}, {J, K}}

This won't allow the ... (e.g. A, ..., E), for that, more work is needed.

The ext.node-families library allows you to put all sublayout nodes in one family of the same width, though this will need two compilation runs.

The \cnt macro is not available when the label (or the options of the sublayout) are processed which is why I have added them in the last step.

Code

\documentclass[tikz]{standalone}
\usetikzlibrary{graphdrawing, graphs, quotes, backgrounds}
\usetikzlibrary{ext.node-families}
\usegdlibrary{layered}
\pgfqkeys{/utils/count list}{.style 2 args={/utils/exec=\def#2{0},
  /utils/temp/.code=\edef#2{\pgfinteval{#2+1}},/utils/temp/.list={#1}}}
\tikzset{
  flowchart/nodes/.style={
    draw=blue!25!red, fill=blue!50!red!50,
    text width=width("$M$"), align=center},
  flowchart/boxes fg/.style={outer sep=+0pt, /tikz/node family/width=sublayout},
  flowchart/boxes bg/.style={draw=yellow!50!black, fill=yellow!20}}
\newcommand*\tikzsimpleflowchart[2][]{%
\begin{tikzpicture}[
  subgraph nodes={/tikz/flowchart/boxes fg},
  subgraph text none, label position=left,
  /utils/count list={#2}{\itemsinlist},#1]
\graph[math nodes, nodes={/tikz/flowchart/nodes}, layered layout]{
  \foreach[
    count=\cnt,
    remember=\listitem as \lastitem (initially )]\listitem in {#2}{
    w\cnt //[layered layout]{[parse/.expand once=\listitem]},
    {[parse/.expand once=\lastitem]}
      ->[complete bipartite]
        {[parse/.expand once=\listitem]}}};
\scoped[on background layer]\foreach \cnt in {1,...,\itemsinlist}
  \path[flowchart/boxes bg]
    (w\cnt.south west) rectangle (w\cnt.north east)
    [late options={name=w\cnt,label=$w_{\cnt}$}];
\end{tikzpicture}}
\begin{document}
\begin{tikzpicture}[
  subgraph nodes={outer sep=+0pt},
  subgraph text none,
  label position=left]
\graph[
  math nodes,
  nodes={draw=blue!25!red, fill=blue!50!red!50},
  layered layout
]{
  w1["$w_1$"] //[layered layout] {A, B, C},
  w2["$w_2$"] //[layered layout] {D, E},
  w3["$w_3$"] //[layered layout] {F};
  {A, B, C} ->[complete bipartite] {D, E} -> F
};
\scoped[on background layer]\foreach \w in {1,...,3}
  \path[draw=yellow!50!black, fill=yellow!20]
    (w\w.south west) rectangle (w\w.north east);
\end{tikzpicture}
\tikzsimpleflowchart{{A, B, C, D, E}, {F, G, H}, {I}, {J, K}}
\end{document}

Output

Answer 2

Another basic solution that also works with the pdfLaTeX engine:

\documentclass[margin=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,
                backgrounds,
                fit,
                positioning}
\begin{document}
    \begin{tikzpicture}[
node distance = 7mm and 7mm,
     N/.style = {draw, draw=purple, fill=purple!30,
                 minimum size=5mm, inner sep =1mm}, 
  FIT/.style = {draw, draw=yellow, fill=yellow!30,
                inner sep=2mm, fit=#1},

every edge/.append style = {-{Straight Barb[scale=0.8]}, semithick}
                        ]
\node[N]   (w11) {A};
\node[N, right=of w11]      (w12) {B};
\node[N, right=of w12]      (w13) {B};
%
    \begin{scope}[node distance = 7mm and 0mm]
\node[N, below right=of w11] (w21) {C};
\node[N, below right=of w12] (w22) {D};
%
\node[N, below right=of w21] (w31) {E};
    \end{scope}
%
    \begin{scope}[on background layer]
\node[FIT=(w11) (w13), label=left:$w1$] {};
\node[FIT=(w21) (w22), label=left:$w2$] {};
\node[FIT=(w31), label=left:$w3$] {};
    \end{scope}
\foreach \i in {1,2,3}
{   \draw   (w1\i) edge (w21);
    \draw   (w1\i) edge (w22);
 \ifnum\i<3
    \draw   (w2\i) edge (w31);
 \fi
}
    \end{tikzpicture}
\end{document}