I need help in the pictures below.
I can not draw the rounded rectangle upon the two axes, the line like U in the pictures on the left, and the line bounded the elements in the picture on the right.
Here is my attempt.
\begin{tikzpicture}[every node/.append style={font=\sffamily\footnotesize}] \begin{axis}[
axis y line = left,
axis x line = bottom,
xtick = {1,2,...,6},
ytick = {1,2,3},
ticklabel style = {font = \sffamily\footnotesize},
grid,
grid style = {color=gray, dotted},
xmin = 0, xmax = 6.5,
ymin = 0, ymax = 2.5,
]
\draw[fill=blue!70, draw=blue!80] (axis cs:1,1) circle (0.1cm);
\draw[fill=blue!70, draw=blue!80] (axis cs:2,1) circle (0.1cm);
\draw[fill=blue!70, draw=blue!80] (axis cs:3,2) circle (0.1cm);
\draw[fill=blue!70, draw=blue!80] (axis cs:5,2) circle (0.1cm);
\end{axis} \end{tikzpicture}