So I have multiple data frames and I'm trying to calculate the sum of specific columns and store within a new column in the data frame for EACH data frame and I'm not sure how to go about it. So far, I can run a for loop for a single dataframe:
for (i in nrow(df1)){df1$newcolumn <-(df1$a + df1$b + df1$c)}
But if I have multiple data frames (df1,df2,df3,...), how do I do this? The column names are the same for each dataframe.
Thank you!
If your dataframe is called df1, df2 etc, you can use this pattern to get dataframe in a list using mget and add a new column in each dataframe using transform.
new_data <- lapply(mget(ls(pattern = 'df\\d+')), function(df)
transform(df, newcolumn = a + b + c))
This will return list of dataframes, if you want them as individual dataframes again use list2env.
list2env(new_data, .GlobalEnv)
Two other approaches.
# create example data
df1 <- df2 <- data.frame(x=1:4, y=1:4)
# put into a list
l <- list(df1, df2)
# iterate over the list with a for loop
for(i in 1:length(l)){
l[[i]]$new_column <- l[[i]]$x + l[[i]]$y
}
# same as above, but using `lapply()` and an anonymous function
# this requires you have the package `dplyr`
lapply(l, function(j) dplyr::mutate(j, new_column = x + y))
both return:
[[1]]
x y new_column
1 1 1 2
2 2 2 4
3 3 3 6
4 4 4 8
[[2]]
x y new_column
1 1 1 2
2 2 2 4
3 3 3 6
4 4 4 8
And as shown above, to access individual list elements, which we've made data.frames in this example, use double bracket notation ([[):
> l[[1]]
x y new_column
1 1 1 2
2 2 2 4
3 3 3 6
4 4 4 8
With tidyverse, we can do
library(dplyr)
library(purrr)
new_data <- lmget(ls(pattern = '^df\\d+$')) %>%
map(~ .x %>%
mutate(newcolumn = a + b + c))
if we need individual datasets
list2env(new_data, .GlobalEnv)
