如何制作一个循环以从 1000 个数据帧中获取一个变量

Question

I have dataframe by name V1...V1000. inside the dataframe each has one variable with the same name 'var1.predict'. I'm having a hard time creating a loop in order to concatenate all the variables I want to fetch into one new dataframe

this is the syntax I want to make a loop

df <- cbind.data.frame(model_V1$var1.pred,model_V2$var1.pred,.....model_V1000$var1.pred)

I hope someone can help solve this. thank you

a new dataframe formed by taking one variable from each dataframe

Answer 1

I assume that you mean you have 1,000 dataframes V1... V1000 each with the column var1.predict and you want to extract the predictions column from each df. If so, there are a few methods outlined below with a little reprex:

# putting dummy data in to the global env
lapply(1:3, \(i) {
  assign(paste0("V", i), data.frame(v1 = rnorm(5), 
                                    v2 = rnorm(5), 
                                    var1.predict = rnorm(5)), envir = .GlobalEnv)
})

df_list <- list(V1, V3, V3)

# using a for loop and do.call
pred_cols <- list()
for (df in df_list) {
  pred_cols <- c(pred_cols, list(df[["var1.predict"]]))
}
pred_cols_df <- do.call(cbind, pred_cols) 
as.data.frame(pred_cols_df)
pred_cols_df


# using a loop without do.call
for (i in seq_along(df_list)) {
  if (i == 1) {
    pred_cols_df <- df_list[[1]][["var1.predict"]]
  } else {
    pred_cols_df <- cbind(pred_cols_df, df_list[[i]][["var1.predict"]])
  }
}
as.data.frame(pred_cols_df)
pred_cols_df

# using lapply
pred_cols <- lapply(df_list, `[`, "var1.predict")
pred_cols_df <- do.call(cbind, pred_cols)
as.data.frame(pred_cols_df)
pred_cols_df