从 lat/lon 坐标中减去数据

Question

我有 2 个数据文件，如下所示：

Model Data
long  lat   count
96.25 18.75     4
78.75 21.25     3
86.75 23.25     7
91.25 33.75     10

Observation Data
long  lat   count
96.75 25.75    10
86.75 23.25     7
78.75 21.25    11
95.25 30.25     5

我正在尝试减去匹配的 lat/long 组合（模型数据-观察数据）的计数，以便 78.75 和 21.25 的第一个组合给出 -8 的差异计数。任何没有匹配项的 lat/long 点都将被减去或从 0 中减去。

我尝试了一个 if 语句来匹配减法点：

if (modeldata$long == obsdata$long & modeldata$lat == obsdata$lat) {
      obsdata$difference <- modeldata$count - obsdata$count
 }

但是，这只是按顺序减去行，而不是按匹配点减去，除非匹配点恰好落在同一行内。

我也收到这些警告：

Warning messages:

1: In modeldata$long == obsdata$long : longer object length is not a multiple of shorter object length

2: In modeldata$lat == obsdata$lat : longer object length is not a multiple of shorter object length

3: In if (modeldata$long == obsdata$long & modeldata$lat == : the condition has length > 1 and only the first element will be used

如有任何帮助，我们将不胜感激！

Answer 1

您可以使用 data.table 加入和更新

library(data.table)

## reading your supplied data
# dt_model <- fread(
#   'long  lat   count
# 96.25 18.75     4
#   78.75 21.25     3
#   86.75 23.25     7
#   91.25 33.75     10'
# )
# 
# 
# dt_obs <- fread(
# "long  lat   count
#   96.75 25.75    10
#   86.75 23.25     7
#   78.75 21.25    11
#   95.25 30.25     5"
# )

setDT(dt_model)
setDT(dt_obs)

## this join & update will update the `dt_model`. 
dt_model[ 
    dt_obs
    , on = c("long", "lat")
    , count := count - i.count
    ]

dt_model
#     long   lat count
# 1: 96.25 18.75     4
# 2: 78.75 21.25    -8
# 3: 86.75 23.25     0
# 4: 91.25 33.75    10

注意到加入坐标 (floats/decimals) 可能并不总是给出正确答案的明显警告

Answer 2

您可以合并坐标，为 NA 加 0 并减去。

mdl <- read.table(text = "long  lat   count
96.25 18.75     4
78.75 21.25     3
86.75 23.25     7
91.25 33.75     10", header = TRUE)

obs <- read.table(text = "long  lat   count
96.75 25.75    10
                  86.75 23.25     7
                  78.75 21.25    11
                  95.25 30.25     5", header = TRUE)

xy <- merge(mdl, obs, by = c("long", "lat"), all.x = TRUE)

xy[is.na(xy)] <- 0

xy$diff <- xy$count.x - xy$count.y
xy

   long   lat count.x count.y diff
1 78.75 21.25       3      11   -8
2 86.75 23.25       7       7    0
3 91.25 33.75      10       0   10
4 96.25 18.75       4       0    4

Answer 3

这里有一个选项dplyr

library(dplyr)
left_join(mdl, obs, by = c("long", "lat")) %>%
   transmute(long, lat, count = count.x - replace(count.y, is.na(count.y), 0))
#   long   lat count
#1 96.25 18.75     4
#2 78.75 21.25    -8
#3 86.75 23.25     0
#4 91.25 33.75    10

从 lat/lon 坐标中减去数据

Subtract data from lat/lon coordinates

if-statement

r

latitude-longitude

dataframe