Question

I have two dataframes and I wish to insert the values of one dataframe into another (let’s call them DF1 and DF2).

DF1 consists of 2 columns 1 and 2. Column 1 (col1) contains characters a to z and col2 has values associated with each character (from a to z)

DF2 is a dataframe with 3 columns. The first two consist of every combination of DF1$col1 so: aa ab ac ad etc; where the first letter is in col1 and the second letter is in col2

I want to create a simple mathematical model utilizing the values in DF1$col2 to see the outcomes of every possible combination of objects in DF1$col1
The first step I wanted to do is to transfer values from DF1$col2 to DF2$col3 (values from DF2$col3 should be associated to values in DF2col1), but that’s where I’m stuck. I currently have

for(j in 1:length(DF2$col1))
{
  ## this part is to use the characters in DF2$col1 as an input 
  ## to yield the output for DF2$col3--
  input=c(DF2$col1)[j]

  ## This is supposed to use the values found in DF1$col2 to fill in DF2$col3

  g=DF1[(DF1$col2==input),"pred"]

  ## This is so that the values will fill in DF2$col3--
  DF2$col3=g
}

When I run this, DF2$col3 will be filled up with the same value for a specific character from DF1 (e.g. DF2$col3 will have all the rows filled with the value associated with character “a” from DF1)
What exactly am I doing wrong?

Thanks a bunch for your time

Answer 1

You should really use merge for this as @Aaron suggested in his comment above, but if you insist on writing your own loop, than you have the problem in your last line, as you assign g value to the whole col3 column. You should use the j index there also, like:

for(j in 1:length(DF2$col1))
{
  DF2$col3[j] = DF1[(which(DF1$col2 == DF2$col1[j]), "pred"]
}

If this would not work out, than please also post some sample database to be able to help in more details (as I do not know, but have a gues what could be "pred").