How to select rows according to column value conditions

Question

I have a data set which looks like the following (partially):

id  name    dummy
1   Jane    1
1   Jane    0
1   Jane    1
2   Mike    0
2   Mike    0
2   Mik         


        

Answer 1

You can use plyr::ddply too

require(plyr)
ddply(df, .(name), function(x) subset(x, !all(dummy == 0)))
##   id name dummy
## 1  1 Jane     1
## 2  1 Jane     0
## 3  1 Jane     1
## 4  3  Tom     1
## 5  3  Tom     1
## 6  3  Tom     0
## 7  3  Tom     0

Note that it's possible to replace !all(dummy == 0) by any(dummy != 0)