Pelle - 9 days ago 5

R Question

I like to average out values from a data.frame that are smaller than their neighbors. This is the example:

`df <- data.frame(V1 = c(1:10), V2 = c(0.5, 1, 2, 6, 7, 6.5, 8, 8.2, 8.1, 8.5))`

for (i in 2:(nrow(df)-1)) {

df[i,2] <- ifelse(

df[i,2] < df[i+1,2] & df[i,2] < df[i-1,2],

mean(c(df[i+1,2], df[i-1,2])),

df[i,2]

)

}

Is there a better way to omit the for-loop?

Thanks in advanced!

Answer

You could do this vectorized:

```
inds <- which(with(df, V2<c(NA,head(V2,-1)) & V2<c(tail(V2,-1),NA)))
#[1] 6 9
df$V2[inds] <- (df$V2[inds-1]+df$V2[inds+1])/2
# V1 V2
# 1 1 0.50
# 2 2 1.00
# 3 3 2.00
# 4 4 6.00
# 5 5 7.00
# 6 6 7.50
# 7 7 8.00
# 8 8 8.20
# 9 9 8.35
# 10 10 8.50
```