R - Insert value into new row based on another dataframe

Question

Dataframe_1

    Name  Value
    a      4
    b      5
    c      7
    d      9

Dataframe_2

I want the following result:

   Name  Value   Mass
   a      4      131
   b      5      110
   c      7      140
   d      9      90

I did this originally as the following but now I have dataframe_2 that I want to get the value from

   Dataframe_1$Mass <- gsub("a", 131, Dataframe_1$Name)

Thank you for your help

score 2 · Answer 1 · answered Aug 14 '18 at 19:47

2

e.g. if your two data.frames are called dt1 and dt2, you would use dtnew <- merge(dt1, dt2, by = "Name")

There are variables for controlling different types of joins e.g. How to join (merge) data frames (inner, outer, left, right)?

answered Aug 14 '18 at 19:47

Jonny Phelps

Fwwiw, for future-proofing answers, folks usually refer to `?merge` instead of external links. – Frank Aug 14 '18 at 19:50
Thank you for your solution Jonny – J_Throat Aug 14 '18 at 19:58

Hatt · Accepted Answer · 2018-08-14T19:55:38.280

1

You're just looking to merge them? I would just merge:

merged <- merge(dataframe_1,dataframe_2, by="Name", all=TRUE) #all
merged <- merge(dataframe_1,dataframe_2, by="Name", all.x =TRUE) #dataframe 1 full

edited Aug 14 '18 at 19:55

answered Aug 14 '18 at 19:46

Hatt

Not all values in dataframe_1 are found in dataframe_2, in other words dataframe_2 is incomplete. In cases where the Name is not in dataframe_2, I don't want to lose the data – J_Throat Aug 14 '18 at 19:53
Gotcha - was just working off the desired set - to get the full outer join use all=TRUE. – Hatt Aug 14 '18 at 19:56
Thank you for your solution Hatt – J_Throat Aug 14 '18 at 19:58
No problem, happy to help when I can. – Hatt Aug 14 '18 at 20:01

2 Answers2