該函數在ddply外部工作正常，但在ddply內部拋出錯誤

Question

我正在嘗試對數據幀進行按行操作（按組）。 當我只為一組運行函數時，它運行得很好。 但是，當我將函數放入ddply以對所有組運行時，會引發錯誤-參數長度為零。

該功能在數據幀“測試”上單獨運行時：

for (i in 1:(nrow(test) - 5)) {

  if (i <= 5) {
    test[i, "MPPALERT"] <- 0    
  }

  FIRSTMPP <- test[i, "TAGMPPSEARCHCOUNT"]
  LASTMPP <- test[i+5, "TAGMPPSEARCHCOUNT"]

  if ((LASTMPP - FIRSTMPP) >= 10) {
    test[i+5, "MPPALERT"] <- 1    
  } else {
    test[i+5, "MPPALERT"] <- 0    
  }

}

ddply中的上述函數將引發錯誤：

Error in if (LASTMPP - FIRSTMPP >= 10) { : argument is of length zero

以下是ddply代碼：

mpp_fn <- function(x) {  

  for (i in 1:(nrow(x) - 5)) {

    if (i <= 5) {
      x[i, "MPPALERT"] <- 0    
    }

    FIRSTMPP <- x[i, "TAGMPPSEARCHCOUNT"]
    LASTMPP <- x[i+5, "TAGMPPSEARCHCOUNT"]

    if (LASTMPP - FIRSTMPP >= 10) {
      x[i+5, "MPPALERT"] <- 1    
    } else {
      x[i+5, "MPPALERT"] <- 0    
    }

  }

}

result <- ddply(data, c("SHELTERID", "INVERTERID"), mpp_fn(x))

在上面的代碼中，FIRSTMPP和LASTMPP的值解析為NULL，因此會出錯，但是為什么會發生這種情況（當它在ddply外部運行得很好時）？

更新：這是dput（data）的輸出：

structure(list(SHELTERID = c("SH02", "SH02", "SH02", "SH02", 
"SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", 
"SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", 
"SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", 
"SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", "SH02", 
"SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", 
"SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", 
"SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", 
"SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", "SH03", 
"SH03", "SH03", "SH03", "SH03"), INVERTERID = c("I1", "I1", "I1", 
"I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", 
"I1", "I1", "I1", "I1", "I2", "I2", "I2", "I2", "I2", "I2", "I2", 
"I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", 
"I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", "I1", 
"I1", "I1", "I1", "I1", "I1", "I1", "I1", "I2", "I2", "I2", "I2", 
"I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", "I2", 
"I2", "I2", "I2"), TAGMPPSEARCHCOUNT = c(0, 0, 0, 0, 0, 0, 0, 
2, 0, 0, 3, 0, 0, 3, 0, 0, 3, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 3, 0, 3, 0, 0, 4, 0, 0, 4, 0, 4, 0, 0, 5, 0, 0, 
5, 0)), .Names = c("SHELTERID", "INVERTERID", "TAGMPPSEARCHCOUNT"
), row.names = c(350L, 351L, 352L, 353L, 354L, 355L, 356L, 357L, 
358L, 359L, 360L, 361L, 362L, 363L, 364L, 365L, 366L, 367L, 494L, 
495L, 496L, 497L, 498L, 499L, 500L, 501L, 502L, 503L, 504L, 505L, 
506L, 507L, 508L, 509L, 510L, 511L, 638L, 639L, 640L, 641L, 642L, 
643L, 644L, 645L, 646L, 647L, 648L, 649L, 650L, 651L, 652L, 653L, 
654L, 655L, 782L, 783L, 784L, 785L, 786L, 787L, 788L, 789L, 790L, 
791L, 792L, 793L, 794L, 795L, 796L, 797L, 798L, 799L), class = "data.frame")

Answer 1

這是dplyr解決方案。 它不需要顯式循環

library(dplyr)
data %>% 
  group_by(SHELTERID, INVERTERID) %>% 
  mutate(
    First = lag(TAGMPPSEARCHCOUNT, 5), 
    MPPALERT = ifelse(
      is.na(First),
      0,
      ifelse(
        TAGMPPSEARCHCOUNT - First > 10, 
        1, 
        0
      )
    )
  )