CODEWITHSUNDEEP
rfunctionapproximationinterpolation
Robert Jefferies
Robert Jefferies

Reputation: 89

Can I use the R approx() function to return a different value then what is being interpolated?

So basically I have a large data frame to two columns, one time column and one size column. I then have another data frame with just one time column. I want to interpolate the times from the data frame with just times into the other data frame, and I then want to return the sizes corresponding to the time that was just interpolated.

Example:

Table 1:

Time
2
4

Table 2:

Time   Size
1      40
3      50
5      30

I basically want to interpolate the "2" from table 1 in between the "1" and "3" in table two, and return the sizes "40" and "50"

How do I do this using the approx function?

Upvotes: 1

Views: 4972

Answers (1)

G. Grothendieck
G. Grothendieck

Reputation: 269526

Try this:

> Table1 <- data.frame(Time = c(2, 4))
> Table2 <- data.frame(Time = c(1, 3, 5), size = c(40, 50, 30))
> approx(Table2$Time, Table2$size, xout = Table1$Time, method = "constant")
$x
[1] 2 4

$y
[1] 40 50

ADDED. This can also be done using the zoo package like this:

> library(zoo)
> z2 <- read.zoo(Table2, FUN = identity)
> na.approx(z2, xout = Table1$Time, method = "constant")
 2  4 
40 50

In the future please write out your input data in R so it can simply be copied and pasted into a running R session as we have done above.

Upvotes: 3

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