Hi All
I've gotten some awesome help getting a formular that finds the intersection of
two vectors. This works brilliantly, but I can't figure out how to make it run
over another factor. A simple example looks likes this:
df <- data.frame(
id = factor(rep(c("supply", "demand"), each = 10)),
price = c(5,7,9,11,13,15,17,19,21,23,20,18,16,14,12,10,8,6,4,2 ),
quantity = c(3,5,7,13,19,31,37,53,61,67,6,18,20,24,40,46,66,70,76,78)
)
quantity_points <- with(
df,
seq(min(quantity), max(quantity), length.out = 500)
)
by_id <- split(df[, c("price", "quantity")], df$id)
interpolated_price <- lapply(
by_id,
function(x)
{
with(
x,
approx(
quantity,
price,
xout = quantity_points
)
)$y
}
)
index_of_equality <- with(interpolated_price, which.min(abs(supply - demand)))
quantity_points[index_of_equality]
Question: I need to run this over a larger data frame, where I have the same
data, but also a new factor variable (called hour). So if you have the original
data frame and add:
df <- data.frame(
hour = factor(seq(1:20)),
id = factor(rep(c("supply", "demand"), each = 10)),
price = c(5,7,9,11,13,15,17,19,21,23,20,18,16,14,12,10,8,6,4,2 ),
quantity = c(3,5,7,13,19,31,37,53,61,67,6,18,20,24,40,46,66,70,76,78)
)
How can I run it for each hour? I tried using:
by_hour <- split(df[, c("price", "quantity")], df$hour)
mapply(fx, by_hour)
And gathering the above into a fx <- function(){"the neat code"}, but I can't
get it to work.
Kind Regards,
Lasse
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