如何修复`$<-.data.frame`替换有x行，数据有y行错误？
如何修复`$<-.data.frame`替换有x行，数据有y行错误？
提问于 2019-09-12 18:42:07
我的目标是创建一个for循环，将数据集中的某些特定列转换为因子或整数。
条件将基于列的名称。
# Here is a small reproducible dataset
df <- data.frame(x = c(10,20,30), y = c("yes", "no", "no"), z = c("Big", "Small", "Average"))
# here is a vector that we are going to use inside our if statement
column_factor_names <- c("y", "z")
# for each column in df
for (i in names(df)) {
print(i)
# if it's a factor, convert into factor, else convert it into integer
if (i %in% column_factor_names) {
print("it's a factor")
df$i <- as.factor(df$i)
} else {
print("it's an integer")
df$i <- as.integer(df$i)
}
}当我运行这个命令时，我得到：Error in `$<-.data.frame`(`*tmp*`, "i", value = integer(0)) : replacement has 0 rows, data has 3
问题出在if-else语句中的df$i <- as.factor(df$i)和df$i <- as.integer(df$i)行。
但我不明白的是，当我手动运行它时。例如：
df$"x" <- as.integer(df$"x")
df$"y" <- as.factor(df$"y")
df$"z" <- as.factor(df$"z")
str(df)它正在工作：
'data.frame': 3 obs. of 3 variables:
$ x: int 10 20 30
$ y: Factor w/ 2 levels "no","yes": 2 1 1
$ z: Factor w/ 3 levels "Average","Big",..: 2 3 1我的问题是:为什么它不能在for-loop和if语句中工作？
回答 2
Stack Overflow用户
回答已采纳
发布于 2019-09-12 18:45:59
在您的代码中，子集函数$查找名为i的列，而不是计算i。您可以选择使用[, i]或[[i]]以不同方式设置data.frame的子集
x <- data.frame(x = c(10,20,30), y = c("yes", "no", "no"), z = c("Big", "Small", "Average"))
# here is a vector that we are going to use inside our if statement
column_factor_names <- c("y", "z")
# for each column in df
for (i in names(df)) {
print(i)
# if it's a factor, convert into factor, else convert it into integer
if (i %in% column_factor_names) {
print("it's a factor")
x[[i]] <- as.factor(x[[i]])
} else {
print("it's an integer")
x[[i]] <- as.integer(x[[i]])
}
}更多信息请参见help("$")。
如果你不介意丢失状态消息，你也可以在不需要循环的情况下这样做：
x[, i] <- as.factor(x[, i])Stack Overflow用户
发布于 2019-09-12 19:00:59
为您更正的循环部分代码为：
# Here is a small reproducible dataset
df <- data.frame(x = c(10,20,30), y = c("yes", "no", "no"), z = c("Big", "Small", "Average"))
# here is a vector that we are going to use inside our if statement
column_factor_names <- c("y", "z")
for (i in names(df)) {
print(i)
if (i %in% column_factor_names) {
print("it's a factor")
df[,i] <- as.factor(df[,i])
} else {
print("it's an integer")
df[,i] <- as.numeric(df[,i])
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/57905007
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