This post demonstrates selecting either the last row or the i-th row from each data frame in a list of data frames in R.
the i-th or last rows of data frames within a list
In the following R code, the function collect_ith_or_last_rows() provides a convenient method for selecting either the i-th or last rows of data frames within a list.
# list of data.frames or matrices
list_df_coef <- list(
L = matrix(c(
-0.857, -0.806, -0.731, -0.645,
-0.260, -0.265, -0.262, -0.253,
-0.407, -0.413, -0.408, -0.395),
ncol = 4, byrow = TRUE),
S = matrix(c(
0.001, 0.002, 0.003, 0.004,
0.771, 0.772, 0.773, 0.774,
-0.015, -0.025, -0.035, -0.045),
ncol = 4, byrow = TRUE),
C = matrix(c(
-0.181, -0.178, -0.175, -0.172,
0.045, 0.045, 0.045, 0.045,
0.000, 0.001, 0.001, 0.001),
ncol = 4, byrow = TRUE)
)
list_df_coef
#---------------------------------------------------------------
# When ith_row = i, it selects the ith rows.
# When ith_row is NULL, it defaults to selecting the last rows.
#---------------------------------------------------------------
collect_ith_or_last_rows <- function(df_list, ith_row = NULL) {
# Function to get ith or last row of each data frame
if (is.null(ith_row)) {
get_selected_rows <- function(df) {tail(df, n = 1)}
} else {
get_selected_rows <- function(df) {df[ith_row,,drop=FALSE]}
}
# Apply the function to each data frame in the list
selected_rows <- lapply(df_list, get_selected_rows)
# Combine the selected rows into one data frame
combined_df <- do.call(rbind, selected_rows)
# Set row names based on the names of list ingredients
rownames(combined_df) <- names(df_list)
return(combined_df)
}
collect_ith_or_last_rows(list_df_coef, 1)
collect_ith_or_last_rows(list_df_coef)
The selected results are as follows:
>
> list_df_coef
$L
[,1] [,2] [,3] [,4]
[1,] -0.857 -0.806 -0.731 -0.645
[2,] -0.260 -0.265 -0.262 -0.253
[3,] -0.407 -0.413 -0.408 -0.395
$S
[,1] [,2] [,3] [,4]
[1,] 0.001 0.002 0.003 0.004
[2,] 0.771 0.772 0.773 0.774
[3,] -0.015 -0.025 -0.035 -0.045
$C
[,1] [,2] [,3] [,4]
[1,] -0.181 -0.178 -0.175 -0.172
[2,] 0.045 0.045 0.045 0.045
[3,] 0.000 0.001 0.001 0.001
> collect_ith_or_last_rows(list_df_coef, 1)
[,1] [,2] [,3] [,4]
L -0.857 -0.806 -0.731 -0.645
S 0.001 0.002 0.003 0.004
C -0.181 -0.178 -0.175 -0.172
> collect_ith_or_last_rows(list_df_coef)
[,1] [,2] [,3] [,4]
L -0.407 -0.413 -0.408 -0.395
S -0.015 -0.025 -0.035 -0.045
C 0.000 0.001 0.001 0.001
>
Originally posted on the SHLee AI Financial Model blog.
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