I have two bar charts side by side, and they share the same legend, I have tried to use \addlegendentry{}, but I find my self with a repeated legend!
Here is the code, what should I do (I tried two many solution online but nothing work):
\begin{figure*}[h!]
\begin{adjustbox}{center}
\pgfplotsset{width=0.93\textwidth,height=0.4\textheight,compat=1.16}
\begin{tikzpicture}
\begin{axis}[
legend style={at={(0.5,-0.09)},
anchor=north,legend columns=-1},
symbolic x coords={Precision,Recall,F1-Score,Accuracy},
major tick length=0cm,
xtick=data,
ymin=75.0,
enlarge x limits=0.2,
enlarge y limits={upper,value=0.2},
nodes near coords,
ybar,
every node near coord/.append style={rotate=90, anchor=west},
bar width = 8pt,
]
\addplot
coordinates {(Precision,86.6) (Recall,86.0) (F1-Score,86.3) (Accuracy,98.4)};
\addlegendentry{KNN}
\addplot
coordinates {(Precision,87.6) (Recall,86.2) (F1-Score,86.5) (Accuracy,97.5)};
\addlegendentry{Neural Networks}
\addplot
coordinates {(Precision,85.9) (Recall,86.3) (F1-Score,86.1) (Accuracy,98.6)};
\addlegendentry{Decision Tree}
\addplot
coordinates {(Precision,87.1) (Recall,86.8) (F1-Score,87.0) (Accuracy,99.2)};
\addlegendentry{Random Forest}
\addplot
coordinates {(Precision,85.5) (Recall,82.8) (F1-Score,83.7) (Accuracy,97.4)};
\addlegendentry{SVM}
\addplot
coordinates {(Precision,77.9) (Recall,77.7) (F1-Score,75.9) (Accuracy,87.8)};
\addlegendentry{Naive Bayes}
\end{axis}
\end{tikzpicture}% NO EMPTY LINE HERE!!!!
\begin{tikzpicture}
\begin{axis}[
legend style={at={(0.5,-0.09)},
anchor=north,legend columns=-1},
symbolic x coords={FPR,FNR},
major tick length=0cm,
xtick=data,
ymin=0.0,
enlarge x limits=0.5,
enlarge y limits={upper,value=0.2},
nodes near coords,
ybar,
every node near coord/.append style={rotate=90, anchor=west},
bar width = 15pt,
]
\addlegendentry{KNN}
\addplot
coordinates {(FPR,7.90) (FNR,14.0)};
\addlegendentry{Neural Networks}
\addplot
coordinates {(FPR,3.45) (FNR,13.75)};
\addlegendentry{Decision Tree}
\addplot
coordinates {(FPR,0.39) (FNR,13.63)};
\addlegendentry{Random Forest}
\addplot
coordinates {(FPR,0.31) (FNR,13.13)};
\addlegendentry{SVM}
\addplot
coordinates {(FPR,5.38) (FNR,17.11)};
\addlegendentry{Naive Bayes}
\addplot
coordinates {(FPR,3.63) (FNR,22.19)};
\end{axis}
\end{tikzpicture}
\end{adjustbox}
\caption{Left - No Interaction. Right - Interaction} \label{fig:M}
\end{figure*}


legend to namein theaxisoptions. Have a look for that in the PGFPlots manual section 4.9.7 (v1.17). – Stefan Pinnow May 31 '20 at 13:52