错误，替换有n行，而数据有m

Question

我正在尝试在PCA转换的数据集上运行一个简单的模型。但是，当我尝试映射train.pca['outcome'] = train.df[,'outcome']时，我收到了错误

Error in `[<-.data.frame`(`*tmp*`, "outcome", value = c(1L, 1L, 1L, 1L,  : 
  replacement has 500 rows, data has 32000

以下是完整的错误代码。

library(xgboost)
library(readr)
library(caret)


train.raw = read.csv("file", header = TRUE, sep = ",")
drop = c('column')
train.df = train.raw[, !(names(train.raw) %in% drop)]
train.df[,'outcome'] = as.factor(train.df[,'outcome'])

train.c1 = subset(train.df ,  outcome == 1)
train.c0 = subset(train.df ,  outcome == 0)


fit.pca = prcomp(train.df[,1:100], retx = TRUE, center = T, scale = T)
summary(fit.pca)

train.pca = data.frame(fit.pca$x)
train.pca = train.pca[,1:20]
train.pca['outcome'] = train.df[,'outcome']

我想这与我如何对数据进行子集化有关，但我不确定是什么。任何帮助表示赞赏。