Assign groups with preassigned conditions in R - r

Question

I have such a matrix(df1):
vid col1
103 9
103 3
103 7
103 6
104 7
104 8
104 9
105 6
105 8
106 8
106 9
106 4
106 6
I have another matrix (df2):
vid col1
103 0
104 1
105 5
106 3
I want to assign groups to df1 so that group IDs are conditional on df2 based on vid.
Namely, I would like the following manipulation on df1, desired output:
vid col1 col2
103 9 0
103 3 0
103 7 0
103 6 0
104 7 1
104 8 1
104 9 1
105 6 5
105 8 5
106 8 3
106 9 3
106 4 3
106 6 3
I was trying the following:
df1<-cbind(df1,0)
for (i in 1:nrow(df1)){
for(j in 1:nrow(df2))
{
if(df1[i,1]==df2[j,1]){
df1[i,3]=df2[j,2]
}
else{
df1[i,3]=NA
}
}
}
But this doesn't seem to work, could anyone help me with this please? Thanks!

Answer 1

You can use merge to merge the 2 dataframes together
merge(df1, df2, by='vid')
output would be
vid col1 col2
103 9 0
103 3 0
103 7 0
103 6 0
104 7 1
104 8 1
104 9 1
105 6 5
105 8 5
106 8 3
106 9 3
106 4 3
106 6 3

Answer 2

First, you should make a vector variable, this variable will be the third column of your final data frame.
Vec=vector()
I am assuming here, you have only 4 ID's which are
df2$vid
[1] 103 104 105 106
Now fill the third column while traversing all rows of first data frame df1.
for(i in 1:nrow(df1))
{
if(df1[i,1]==103){Vec[i]=df2[df2$vid==103,2]}
if(df1[i,1]==104){Vec[i]=df2[df2$vid==104,2]}
if(df1[i,1]==105){Vec[i]=df2[df2$vid==105,2]}
if(df1[i,1]==106){Vec[i]=df2[df2$vid==106,2]}
}
Finally, combine the third column with data frame df1.
df1=cbind(df1,Vec)