  The Grains and Oilseeds Index (GOI) and its sub-indices of wheat, maize,
soyabeans, rice, and barley are daily price indexes reflect the price changes
of the global spot markets of staple agro-food crops. In this paper, we carry
out a visibility graph (VG) analysis of the GOI and its five sub-indices. Our
findings reveal that the degree distributions of the VGs, except for rice,
exhibit exponentially truncated power-law tails, while the rice VG conforms to
a power-law tail. The average clustering coefficients of the six VGs are quite
large ($>0.5$) and exhibit a nice power-law relation with respect to the
average degrees of the VGs. For each VG, the clustering coefficients of nodes
are inversely proportional to their degrees for large degrees and are
correlated to their degrees as a power law for small degrees. All the six VGs
exhibit small-world characteristics. The degree-degree correlation coefficients
shows that the VGs for maize and soyabeans indices exhibit weak assortative
mixing patterns, while the other four VGs are weakly disassortative. The
average nearest neighbor degree functions have similar patterns, and each
function shows a more complex mixing pattern which decreases for small degrees,
increases for mediate degrees, and decreases again for large degrees.
