r - 如果列的值以R中的字符“N”开头，如何替换它

Question

如果列的值（GID）以字符“N”开头，如何替换为 ColB，如果 ColB 在 R 编程中的 Dataframe 中为空

代码：

DataFile <- extract_tables("new.pdf",pages = c(87),
                           method = "stream", output = "data.frame", guess = TRUE)
DataFrame<-as.data.frame(DataFile)

#removing No. and A# from columns
df2<-subset(DataFrame, Group!="No." & Group!="A#") 

输出：

GID    ColA    ColB 
1       2       2
2       3       4
3       5       4
4       6       5
5       6       5
NG1     8 
MG2     8       1
MG3     8       1
NG4     8 

预期产出

GID    ColA    ColB 
1       2       2
2       3       4
3       5       4
4       6       5
5       6       5
NG1     8       N
MG2     8       1
MG3     8       1
NG4     8       N

Answer 1

我们可以指定一个条件，例如

i1 <- with(df1, substr(GID, 1, 1) == 'N' & ColB == "")
df1$ColB[i1] <- "N"

---

或使用grepl

i1 <- with(df1,  grepl("^N", GID) & ColB == "")
df1$ColB[i1] <- "N"

---

如果我们想在任何列中替换

i1 <- with(df1, grepl("^N", GID))
nm1 <- setdiff(names(df1), "GID")
df1[nm1] <- lapply(df1[nm1], function(x) replace(x, i1 & x == "", "N"))

-输出

df1
#  GID ColA ColB
#1   1    2    2
#2   2    3    4
#3   3    5    4
#4   4    6    5
#5   5    6    5
#6 NG1    8    N
#7 MG2    8    1
#8 MG3    8    1
#9 NG4    8    N

数据

df1 <-  structure(list(GID = c("1", "2", "3", "4", "5", "NG1", "MG2", 
"MG3", "NG4"), ColA = c(2L, 3L, 5L, 6L, 6L, 8L, 8L, 8L, 8L), 
    ColB = c("2", "4", "4", "5", "5", "", "1", "1", "")), row.names = c(NA, 
-9L), class = "data.frame")