将一列数据框重命名为数字（在R中）

Question

I am looking at 10 different runners, running 10 laps. For each runner, after each lap, I have total used time. For simplicity lets say the data frame looks like this:

> data<-data.frame(runner=c(1:10),lap1=c(1:10),lap2=c(2:11),...,lap10=c(10:20))

The lap times does not make any sense, this is just for the example.

Now, I am creating a function, where one of the arguments of the function is the lap number c:

> func<-function(a,b,c,...) {  }

The parameters a and b, and the list (...) of the function argument is not relevant for my question, but the lap number c is. When I call my function with the argument c , it needs to be a number between 1 and 10.

Now, when I call my function with some argument c, for example c=4, I want to remove the columns called lap1, lap2, lap3, lap5,...,lap10 . So basically I need R to recognize that the argument c equals 4, and then proceeding to remove the columns I am not interested in. I cannot rename the columns.

Thank you for any help!

Answer 1

You can use paste0 to combine a string and a number to a new string:

num <- 4

s <- paste0("lap", num)
# [1] "lap4"

Now, you can remove all but the corresponding column:

data <- data[s]

Answer 2

Okay, so comments got out of hand, here is my answer:

getLapData <- function(data, c) data[c(1, grep(paste0("Lap", c, "_"), names(data)))]
getLapData(data, 1)

Produces:

#       Runner Lap1_test Lap1_real
# 1   Runner 1      2.93      2.19
# 2   Runner 2      2.73      2.58
# 3   Runner 3      1.88       2.2
# 4   Runner 4      1.38      1.06
# 5   Runner 5      1.16      1.79
# 6   Runner 6      2.17      1.21
# 7   Runner 7      1.14      1.05
# 8   Runner 8      2.06      2.68
# 9   Runner 9      1.94      1.65
# 10 Runner 10       1.1      1.59

And here is the data I used:

data <- as.data.frame(cbind(runner=paste("Runner", 1:10), replicate(20, round(runif(10, 1, 3), 2))))
names(data) <- c("Runner", paste0("Lap", rep(1:10, each=2), c("_test", "_real")))