r nested for loop with if statement error message

Question

here the input data and my expectations (y).

# input:
mydf <- data.frame(matrix(1:10, ncol = 2))
x=c(1.5, 2.8, 4.1)
y=c(0, 0, 0)
mydf
x
y

# code
for (i in 1:(length(x))
    for (j in 2:(dim(mydf)[1])
    {{
        if (x[i])>mydf[(j-1),1]) & (x[i])<mydf[j,1]) 
            {y[i]<-mydf[(j-1),2]} 
        else {y[i]<-9999999999}
    }}
y

expectation for y: 6,7,9. I do not understand the error.

You need to place the opening and closing brackets in the right position. That is, for(condition){dostuff}. The same goes for if-statements. And for-loops are not really needed here. — Heroka
– Heroka, Commented Nov 3, 2015 at 16:50

etienne · Accepted Answer · 2015-11-03 18:02:28Z

1

Here is a code that will work and give your expected output :

for (i in 1:length(x)) {
    for (j in 2:nrow(mydf)) {
        if (mydf[j-1,1] < x[i] & x[i] < mydf[j,1]) {
            y[i] <- mydf[j-1,2]    
            break
        } else {y[i]<-9999999999}
    }
}

y

[1] 6 7 9

You need to add the break otherwise j will keep looping and return 9999999999.

A more elegant option would be this :

x=c(1.5, 2.8, 4.1,11)
mydf[nrow(mydf),2]<-999999 # y can't be equal to the lower right cell, so I transform it
y<-mydf[findInterval(x,mydf[,1]),2]
y

y
[1]      6      7      9 999999

An other solution would be this (it is best if some values will return 9999) :

x<-c(-3,1.5, 2.8, 4.1,11)
temp<-sapply(x,function(z){z>mydf[,1]&z<mydf[-1,1]})
temp2<-sapply(seq_along(x),function(z){match(TRUE,temp[,z])})
y<-mydf[temp2,2]
y[is.na(y)]<-9999
y

[1] 9999    6    7    9 9999

edited Nov 3, 2015 at 18:02

answered Nov 3, 2015 at 17:03

etienne

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