user3910073 user3910073 - 2 months ago 8
R Question

R Assign value to column according to value in another column

I have a data frame like this

NAME DIST
A 0
A 1
A 100
A 2
A 1
A 4
A 500
A 1
A 1


What I want to do is to find an efficient way of creating a new column NEWNAME such that if DIST > 100 it contains a a name that is equal for all the previous rows

NAME DIST NEWNAME
A 0 A
A 1 A
A 100 A
A 2 A2
A 1 A2
A 4 A2
A 500 A3
A 1 A3
A 1 A3


I have done it using a for loop but I was looking for a more efficient solution in R style. Below my code using a for loop

k <- 0
for(l in 1:length(df$NAME)){
if(df$DIST[l] >= 100){
k <- k+1;
df$NEWNAME[(l):length(df$NAME)] <- paste(df$NAME,k,sep="")
}
}


Thanks in advance

Answer

You can do this to create your new column:

df$NEWNAME=paste0("A", cumsum(0+df$DIST>=100))

I used your data as df and also assumed you meant superior or equal to 100:

df=data.frame("NAME"=rep("A", 9), "DIST"=c(0,1,100,2,1,4,500,1,1))

EDIT

If you need to start the new names at the row N+1 of the distance>100, you can do this after:

df$NEWNAME2 = lag(df$NEWNAME, n=1, default="A0")
####   NAME DIST NEWNAME NEWNAME2
#### 1    A    0      A0       A0
#### 2    A    1      A0       A0
#### 3    A  100      A1       A0
#### 4    A    2      A1       A1
#### 5    A    1      A1       A1
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