Convert part of the values in rows in a data frame

I have a data frame which looks like this:

df

colA colB
0     0
1     1
0     1
0     1
0     1
1     0
0     0
1     1
0     1

I would like to convert a certain proportion of the 0 in colA to NA and a certain proportion of 1 in colB to NA

if I do this:

df["colA"][df["colA"] == 0] <- NA

all the 0 in columns A will be converted to NA, however I just want half of them to be converted

Similarly, for colB I want only 1/3 of the 1 to be converted:

df["colB"][df["colB"] == 1] <- NA

Expected output:

   colA colB
    0     0
    1     1
    NA    1
    0     1
    NA    1
    1     0
    0     0
    1     NA
    NA    NA

>Solution :

One way

tmp=which(df["colA"]==0)
df$colA[sample(tmp,round(length(tmp)/2))]=NA

similar for colB

tmp=which(df["colB"]==1)
df$colB[sample(tmp,round(length(tmp)/3))]=NA