I have a df such as

```
COL1 COL2 COL3 
A 10 20
B 3 34
C 3 21
D 34 4

```

and I would like to replace all value in `COL2` and `COL3 < 10` by "S"
and all value `>=10` by "N.S"
and get

```
COL1 COL2 COL3 
A N.S N.S
B S N.S
C S N.S
D N.S S

```

I tried :

```
tab$pvalue_cov[tab$COL1<10 ] <- "S"
tab$pvalue_cov[tab$COL1>=10 ] <- "N.S"
tab$pvalue_gc[ tab$COL2<10 ] <- "S"
tab$pvalue_gc[ tab$COL2>=10 ] <- "N.S"

```