Replace certain values of dataframe with values in another dataframe, based on a condition

Question

I have a dataframe like:

> df <- data.frame(id=c(015,335,625,789), B=c(8,19,8,6), C=c(4,1,4,6), Source=c("Gk", "Ap", "Ap", "Kh"))

> df

  id  B C Source
1 015  8 4     Gk
2 335 19 1     Ap
3 625  8 4     Ap
4 789  6 6     Kh

And another dataframe:

p <- data.frame(id=c(335,625, 789), B2 = c(5,3,4))
p

  id B2
1 335  5
2 625  3
3 789  4

I want replace those values in column B of df by the values in B2 of p, but only for those with same id in both dataframes and df$Source == "Ap".

The final dataframe should be:

  id  B C Source
1 015  8 4     Gk
2 335  5 1     Ap
3 625  3 4     Ap
4 789  6 6     Kh

I know how to replace the whole column by zeros or NAs, etc, but I just want to replace those that follow the mentioned condition (and without for loops...). How can I achieve this?

in df your id is not the same as id as in the definition of df. Please edit this. — J_F
– J_F, Commented Jun 8, 2016 at 13:47

Ronak Shah · Accepted Answer · 2016-06-08 13:59:37Z

2

One way is ,

df[df$Source == "Ap", "B"] <- p[p$id %in% df[df$Source == "Ap", "id"] , "B2"]


#   id B C Source
#1  15 8 4     Gk
#2 335 5 1     Ap
#3 625 3 4     Ap
#4 789 6 6     Kh

answered Jun 8, 2016 at 13:59

Ronak Shah

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1 Comment

LRD Over a year ago

That's exactly what I was looking for. Thanks!

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