I would like to keep the part after the FIRST undescore. Please see example code. 

```
colnames(df)
"EGAR00001341740_P32_1"    "EGAR00001341741_PN32"

```

My try, but does not give `P32_1` but only `P32` which is wrong.

```
sapply(strsplit(colnames(df), split='_', fixed=TRUE), function(x) (x[2]))

```

desired output: `P32_1, PN32`