在ggplot2上製作圖例

Question

如何在此代碼中添加圖例？

謝謝！

ggplot()+ 
    geom_point(data=avg_harv_df, aes(x=samp_per, y=ndvi), size=3, color='red') + 
    geom_point(data=avg_sjer_df, aes(x=samp_per, y=ndvi), size=3, color='blue') + 
    ylab("NDVI")+ 
    xlab("Sampling period") 

Answer 1

選項1：

ggplot()+ 
    geom_point(data=avg_harv_df, aes(x=samp_per, y=ndvi, col = "a"), size=3) + 
    geom_point(data=avg_sjer_df, aes(x=samp_per, y=ndvi, col = "b"), size=3) + 
    ylab("NDVI")+ 
    xlab("Sampling period") 

選項2：

combined <- dplyr::bind_rows(avg_harv_df, avg_sjer_df, .id = 'col') 
ggplot(combined, aes(x=samp_per, y=ndvi, col = col))+ 
    geom_point(size=3) + 
    ylab("NDVI")+ 
    xlab("Sampling period") 

我幾乎總是喜歡選項2