\documentclass[tikz,border=5pt]{standalone}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{pgfplots}
\usetikzlibrary{positioning}
\pgfplotsset{compat=1.15}
\usepgfplotslibrary{statistics}
\usepgfplotslibrary{groupplots}
\begin{document}
\begin{tikzpicture}[]
\begin{groupplot}[group style={vertical sep = 0.5cm, horizontal sep = 1.0cm, group size=2 by 2}]\nextgroupplot [legend style = {at={(0.1,1.15)}, anchor=west}, ylabel = {avg. AUC}, width=5cm, height=3cm, scale only axis=true, xtick={1,2,3,4,5,6,7}, xticklabels={}, legend columns = -1]\addplot+ coordinates { (1.0, 0.7980000000000002) (2.0, 0.833) (3.0, 0.8539999999999999) (4.0, 0.8677499999999998) (5.0, 0.8722499999999996) (6.0, 0.8722499999999996) (7.0, 0.9037499999999999) };
\addplot+ coordinates { (1.0, 0.8317499999999999) (2.0, 0.84375) (3.0, 0.8617500000000001) (4.0, 0.8727499999999999) (5.0, 0.88125) (6.0, 0.8887499999999999) (7.0, 0.916) };
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\addplot+ coordinates { (1.0, 0.6847499999999999) (2.0, 0.7514999999999998) (3.0, 0.8084999999999999) (4.0, 0.8265) (5.0, 0.83375) (6.0, 0.8442500000000001) (7.0, 0.8867499999999999) };
\addplot+ coordinates { (1.0, 0.79725) (2.0, 0.81325) (3.0, 0.8300000000000001) (4.0, 0.82975) (5.0, 0.8389999999999999) (6.0, 0.8407499999999999) (7.0, 0.8589999999999998) };
\legend{{}{autoencoders}, {}{classical}, {}{gans}, {}{two-stage}, {}{flows}}\nextgroupplot [legend style = {at={(0.1,1.15)}, anchor=west}, width=5cm, height=3cm, scale only axis=true, xtick={1,2,3,4,5,6,7}, xticklabels={}, legend columns = -1]\addplot+ coordinates { (1.0, 0.6325000000000001) (2.0, 0.65) (3.0, 0.6825000000000001) (4.0, 0.7) (5.0, 0.72) (6.0, 0.73) (7.0, 0.76) };
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\nextgroupplot [ylabel = {avg. rank}, xtick={1,2,3,4,5,6,7}, xticklabels={$PR@\#5$,$PR@\#10$,$PR@\#50$,$PR@\#100$,$PR@\#500$,$PR@\#1000$,$AUC_{val}$}, width=5cm, height=3cm, scale only axis=true, x tick label style={rotate=50,anchor=east}]\addplot+ coordinates { (1.0, 2.7) (2.0, 2.7) (3.0, 2.7) (4.0, 2.5) (5.0, 2.4) (6.0, 2.4) (7.0, 2.1) };
\addplot+ coordinates { (1.0, 2.3) (2.0, 2.1) (3.0, 1.9) (4.0, 2.0) (5.0, 2.0) (6.0, 1.9) (7.0, 1.5) };
\addplot+ coordinates { (1.0, 3.3) (2.0, 3.6) (3.0, 3.6) (4.0, 3.8) (5.0, 3.8) (6.0, 3.8) (7.0, 3.7) };
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\nextgroupplot [xtick={1,2,3,4,5,6,7}, xticklabels={$PR@\#5$,$PR@\#10$,$PR@\#50$,$PR@\#100$,$PR@\#500$,$PR@\#1000$,$AUC_{val}$}, width=5cm, height=3cm, scale only axis=true, x tick label style={rotate=50,anchor=east}]\addplot+ coordinates { (1.0, 2.5) (2.0, 3.0) (3.0, 2.8) (4.0, 2.5) (5.0, 2.8) (6.0, 2.5) (7.0, 2.2) };
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\end{groupplot}
\end{tikzpicture}
\end{document}