How to make multiple similar size circles randomly within specified square /triangular area?

Question

I would like to have multiples circles drawn randomly within specified square area or triangular area. I tried a method explained by tikz: Distribute evenly and randomly circles with fixed starting point of square as (0,0). I modified it for my requirement which has some error. Modified code is

\documentclass[]{article}
\usepackage{tikz}
\usetikzlibrary{backgrounds}
\begin{document}
    % Here #1, #2 -- start of rectanle coordinates (x,y)
    % #3, #4 -- other end  of rectanle coordinates (x,y)
    %   #5, #6 -- circle radius and count(number) of circles.
\def\xlist{6}
\def\ylist{6}

\newcommand{\fillrandomly}[6]{
    \pgfmathsetmacro\diameter{#3*2}
    \draw (#1,#2) rectangle (#3,#4);
    \foreach \i in {1,...,#6}{
        \pgfmathsetmacro\x{rnd*#3}
        \pgfmathsetmacro\y{rnd*#4}
        \xdef\collision{0}
        \foreach \element [count=\i] in \xlist{
            \pgfmathtruncatemacro\j{\i-1}
            \pgfmathsetmacro\checkdistance{ sqrt( ({\xlist}[\j]-(\x))^2 + ({\ylist}[\j]-(\y))^2 ) }
            \ifdim\checkdistance pt<\diameter pt
            \xdef\collision{1}
            \breakforeach
            \fi
        }
        \ifnum\collision=0
        \xdef\xlist{\xlist,\x}
        \xdef\ylist{\ylist,\y}
        \draw [black, fill=gray, thick] (\x,\y) circle [radius=#5];
        \fi 

    }
}   

         \pgfmathsetseed{2}
     \fillrandomly{0.25}{2}{2}{4}{0.2}{200}

%%%%%%%%

\end{tikzpicture}

\end{figure}
\end{document}

What is wrong in this code? Here is my poor code for generating required image

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{figure}[htbp]
    \centering
        %   \resizebox{0.98\textwidth}{!}{%
    \begin{tikzpicture} [every text node part/.style={align=center}, font=\scriptsize]
        \draw [->] (0,0) -- node[anchor=south] {x}  (4,0);
        \draw [->] (0,0) -- node[anchor = east] {y}  (0,4);
        \draw[ help lines,line width=0.005pt,step=0.5] (0,0) grid (4,4);
    \draw (0.25, 2) rectangle (2,4);
     \tikzset{my_circle/.style={circle, inner sep=0pt, minimum size=0.15cm, black,fill=gray, draw=none}};

     \node[my_circle] at (0.5,2. 3) {};
     \node[my_circle] at (0.8,2.3) {};
     \node[my_circle] at (1,2.5) {};
     \node[my_circle] at (1.4,3) {};
     \node[my_circle] at (1.5,3.5) {};
     \node[my_circle] at (1.5,3.8) {};
     \node[my_circle] at (1.8,3.7) {};
     \node[my_circle] at (1.5,3.5) {};
     \node[my_circle] at (1,3) {};
     \node[my_circle] at (0.6,3) {};
     \node[my_circle] at (0.4,3.5) {};
     \node[my_circle] at (1.8,2.6) {};
     \node[my_circle] at (1.5,2.2) {};
     \node[my_circle] at (0.8,3.8) {};
\end{tikzpicture}

\end{figure}
\end{document}