根据r中字符串的中间位置对文件进行数字排序

Question

我在一个目录中有一个.tif图像列表，稍后我会循环浏览该列表以进行一些光栅计算。我希望.tif文件按日期排序，这样当循环运行时，我就可以根据列表中的顺序知道哪个日期对应于哪个.tif文件。我想我需要重命名这些文件，或者想办法在循环后对它们进行排序。

例如：

rastlist <- list.files(here::here("data", "s2_cropped"), 
pattern = '.tif$', all.files = TRUE, full.names = TRUE)
rastlist
[1] "/data/s2_cropped/S2A2A_20200307_135_36MYD_BOA_10.tif"
[2] "/data/s2_cropped/S2A2A_20200605_135_36MYD_BOA_10.tif" 
[3] "/data/s2_cropped/S2A2A_20200705_135_36MYD_BOA_10.tif" 
[4] "/data/s2_cropped/S2A2A_20200804_135_36MYD_BOA_10.tif" 
[5] "/data/s2_cropped/S2A2A_20200903_135_36MYD_BOA_10.tif" 
[6] "/data/s2_cropped/S2A2A_20201003_135_36MYD_BOA_10.tif" 
[7] "/data/s2_cropped/S2A2A_20201102_135_36MYD_BOA_10.tif" 
[8] "/data/s2_cropped/S2A2A_20201202_135_36MYD_BOA_10.tif" 
[9] "/data/s2_cropped/S2B2A_20200102_135_36MYD_BOA_10.tif" 
[10] "/data/s2_cropped/S2B2A_20200211_135_36MYD_BOA_10.tif" 
[11] "/data/s2_cropped/S2B2A_20200401_135_36MYD_BOA_10.tif" 
[12] "/data/s2_cropped/S2B2A_20200501_135_36MYD_BOA_10.tif" 

我认为它是根据字符串"的第一部分按字母顺序排序的；S2A2A"&quot；S2B2A"；，但我想在这样的日期前订购：

rastlist
[1] "/data/s2_cropped/S2B2A_20200102_135_36MYD_BOA_10.tif" 
[2] "/data/s2_cropped/S2B2A_20200211_135_36MYD_BOA_10.tif"
[3] "/data/s2_cropped/S2A2A_20200307_135_36MYD_BOA_10.tif"
[4] "/data/s2_cropped/S2B2A_20200401_135_36MYD_BOA_10.tif" 
[5] "/data/s2_cropped/S2B2A_20200501_135_36MYD_BOA_10.tif"
[6] "/data/s2_cropped/S2A2A_20200605_135_36MYD_BOA_10.tif" 
[7] "/data/s2_cropped/S2A2A_20200705_135_36MYD_BOA_10.tif" 
[8] "/data/s2_cropped/S2A2A_20200804_135_36MYD_BOA_10.tif" 
[9] "/data/s2_cropped/S2A2A_20200903_135_36MYD_BOA_10.tif" 
[10] "/data/s2_cropped/S2A2A_20201003_135_36MYD_BOA_10.tif" 
[11] "/data/s2_cropped/S2A2A_20201102_135_36MYD_BOA_10.tif" 
[12] "/data/s2_cropped/S2A2A_20201202_135_36MYD_BOA_10.tif" 

然后我循环遍历，对每个堆栈进行一些光栅计算。我不知道这部分代码是否太重要，但它看起来像这样。

ndvi_list <- list() #empty vector to store ndvi values
for  (i in 1:length(rastlist)) {
b <- brick(rastlist[[i]]
ndvi_list[i] <- (b[[4]] - b[[1]]) / (b[[4]] + b[[1]])
}
The result of the loop is 12 rasters in a list

Answer 1

我们可以提取日期子字符串，转换为Date类、order，并使用该索引对进行排序

rastlist2 <- rastlist[order(as.Date(sub(".*_(\d{8})_.*", 
"\1", rastlist), '%Y%m%d'))]

-输出

rastlist2
#[1] "/data/s2_cropped/S2B2A_20200102_135_36MYD_BOA_10.tif" "/data/s2_cropped/S2B2A_20200211_135_36MYD_BOA_10.tif"
#[3] "/data/s2_cropped/S2A2A_20200307_135_36MYD_BOA_10.tif" "/data/s2_cropped/S2B2A_20200401_135_36MYD_BOA_10.tif"
#[5] "/data/s2_cropped/S2B2A_20200501_135_36MYD_BOA_10.tif" "/data/s2_cropped/S2A2A_20200605_135_36MYD_BOA_10.tif"
#[7] "/data/s2_cropped/S2A2A_20200705_135_36MYD_BOA_10.tif" "/data/s2_cropped/S2A2A_20200804_135_36MYD_BOA_10.tif"
#[9] "/data/s2_cropped/S2A2A_20200903_135_36MYD_BOA_10.tif" "/data/s2_cropped/S2A2A_20201003_135_36MYD_BOA_10.tif"
#[11] "/data/s2_cropped/S2A2A_20201102_135_36MYD_BOA_10.tif" "/data/s2_cropped/S2A2A_20201202_135_36MYD_BOA_10.tif"

数据

rastlist <- c("/data/s2_cropped/S2A2A_20200307_135_36MYD_BOA_10.tif", "/data/s2_cropped/S2A2A_20200605_135_36MYD_BOA_10.tif", 
"/data/s2_cropped/S2A2A_20200705_135_36MYD_BOA_10.tif", "/data/s2_cropped/S2A2A_20200804_135_36MYD_BOA_10.tif", 
"/data/s2_cropped/S2A2A_20200903_135_36MYD_BOA_10.tif", "/data/s2_cropped/S2A2A_20201003_135_36MYD_BOA_10.tif", 
"/data/s2_cropped/S2A2A_20201102_135_36MYD_BOA_10.tif", "/data/s2_cropped/S2A2A_20201202_135_36MYD_BOA_10.tif", 
"/data/s2_cropped/S2B2A_20200102_135_36MYD_BOA_10.tif", "/data/s2_cropped/S2B2A_20200211_135_36MYD_BOA_10.tif", 
"/data/s2_cropped/S2B2A_20200401_135_36MYD_BOA_10.tif", "/data/s2_cropped/S2B2A_20200501_135_36MYD_BOA_10.tif"
)