从文件名中提取日期

Question

我有一个包含 400 多张卫星图像的文件夹，其名称如下：

filenames <- c("mosaic_NDVI_2000_10_15.tif", "mosaic_NDVI_2000_10_31.tif", "mosaic_NDVI_2000_11_16.tif", "mosaic_NDVI_2000_12_18.tif", "mosaic_NDVI_2000_12_2.tif",  "mosaic_NDVI_2000_7_27.tif")

然后，我有一个数据集，需要在最近的日期提取 NDVI 的点坐标，但要做到这一点，我需要将文件名最接近的日期与行日期相匹配。

# example data

df <- data.frame(date = c("2000-7-26", "2000-10-20", "2000-12-10"), lon = c(23.05, 23.12, 23.08), lat = c(-32.56, -32.61, -32.53))
df$date <- lubridate::as_date(df$date)

filenames <- c("mosaic_NDVI_2000_10_15.tif", "mosaic_NDVI_2000_10_31.tif", "mosaic_NDVI_2000_11_16.tif", "mosaic_NDVI_2000_12_18.tif", "mosaic_NDVI_2000_12_2.tif",  "mosaic_NDVI_2000_7_27.tif")

### NEED SOME CODE HERE TO EXTRACT THE DATES AND CREATE THE FOLLOWING VECTOR ###
filename_dates <- c("2000-10-15", "2000-10-31", "2000-11-16", "2000-12-18", "2000-12-2",  "2000-7-27")

filename_dates <- lubridate::as_date(filename_dates)

for(i in 1:nrow(df)){
  date <- df$date[i]
  index <- which(abs(filename_dates - date) == min(abs(filename_dates - date)))
  extraction_filename <- filenames[index]
  point_vec <- vect(df[1,], geom=c("lon", "lat"), crs="+proj=longlat +datum=WGS84", keepgeom=FALSE)
  NDVI <- rast(extraction_filename)
  crs(NDVI) <- crs(point_vec)
  value <- terra::extract(x=NDVI, y=point_vec, df=TRUE)
  df$NDVI[i] <- value[2]}

Answer 1

将文件名转换为数据框并将两者中的日期转换为 Date 类。然后执行指定的 SQL 语句来连接最近的元素。

library(lubridate)
library(sqldf)

filenamesDF <- data.frame(date = ymd(trimws(filenames, whitespace = "\\D")))
df <- transform(df, date = ymd(date))

DF <- sqldf("select a.date, df.date, df.lon, df.lat
  from filenamesDF as a left join df
  on abs(a.date - df.date) = (select min(abs(a.date - df.date)) from df)")
names(DF)[2] <- "date2"
DF

给予

        date      date2   lon    lat
1 2000-10-15 2000-10-20 23.12 -32.61
2 2000-10-31 2000-10-20 23.12 -32.61
3 2000-11-16 2000-12-10 23.08 -32.53
4 2000-12-18 2000-12-10 23.08 -32.53
5 2000-12-02 2000-12-10 23.08 -32.53
6 2000-07-27 2000-07-26 23.05 -32.56

注意

问题的输入

filenames <- c("mosaic_NDVI_2000_10_15.tif", "mosaic_NDVI_2000_10_31.tif", 
  "mosaic_NDVI_2000_11_16.tif", "mosaic_NDVI_2000_12_18.tif", 
  "mosaic_NDVI_2000_12_2.tif",  "mosaic_NDVI_2000_7_27.tif")

df <- data.frame(date = c("2000-7-26", "2000-10-20", "2000-12-10"),
  lon = c(23.05, 23.12, 23.08),
  lat = c(-32.56, -32.61, -32.53)
)