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#install.packages("readr")
library(readr)

github="https://raw.githubusercontent.com/agronomy4future/raw_data_practice/main/fertilizer_treatment.csv"
dataA= data.frame(read_csv(url(github),show_col_types = FALSE))

library(dplyr)
dataB= data.frame(dataA %>%
                    group_by(Genotype, variable) %>%
                    dplyr::summarize(across(c(value), 
                                     .fns= list(Mean = mean, 
                                       SD= sd, 
                                        n= length,
                                       se= ~ sd(.)/sqrt(length(.))))))

dataB
     Genotype    variable value_Mean  value_SD value_n value_se
1  Genotype_A     Control     36.050  7.220572       4 3.610286
2  Genotype_A Fertilizer1     50.625  6.733684       4 3.366842
3  Genotype_A Fertilizer2     45.850  6.943822       4 3.471911
4  Genotype_A Fertilizer3     37.300  7.266820       4 3.633410
5  Genotype_B     Control     50.850 14.552548       4 7.276274
6  Genotype_B Fertilizer1     55.375 11.368487       4 5.684244
7  Genotype_B Fertilizer2     53.100 11.581019       4 5.790509
8  Genotype_B Fertilizer3     54.300  8.504509       4 4.252254
9  Genotype_C     Control     53.925  7.982637       4 3.991319
10 Genotype_C Fertilizer1     51.375  8.327615       4 4.163807
11 Genotype_C Fertilizer2     55.875  9.059939       4 4.529970
12 Genotype_C Fertilizer3     56.050  5.363146       4 2.681573
13 Genotype_D     Control     61.925 10.692482       4 5.346241
14 Genotype_D Fertilizer1     63.425  6.336863       4 3.168432
15 Genotype_D Fertilizer2     57.675 11.139532       4 5.569766
16 Genotype_D Fertilizer3     61.250 11.357670       4 5.678835

ggplot(data=dataB, aes(x=Genotype, y=value_Mean, fill=variable))+
  geom_bar(stat="identity",position="dodge", width=0.9, size=1) +
  geom_errorbar(aes(ymin=value_Mean-value_se, ymax=value_Mean+value_se), 
                position=position_dodge(0.9), width=0.5) +
  scale_fill_manual(values=c("coral4","grey65","darkslategrey","orange"))+
  scale_y_continuous(breaks=seq(0,100,20), limits = c(0,100)) +
  labs(x="Genotype", y=bquote("Grain yield "~Mg~ha^-1*")")) +
  guides(fill = guide_legend(nrow = 2)) +
  theme_classic(base_size=18, base_family="serif")+
  theme(legend.position=c(0.7,0.93),
        legend.title=element_blank(),
        legend.key=element_rect(color="white", fill="white"),
        legend.text=element_text(family="serif", face="plain",
                                 size=15, color= "Black"),
        legend.background=element_rect(fill="white"),
        axis.line=element_line(linewidth=0.5, colour="black"),
        strip.background=element_rect(color="white", 
                                      linewidth=0.5,linetype="solid"))+
windows(width=7.5, height=5)

full code: https://github.com/agronomy4future/r_code/blob/main/In_R%2C_how_do_I_divide_the_legend_into_two_rows_in_a_graph%3F.ipynb

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