I have a dataframe:

```
id
id1
id2
id3
id8
id9
```

I want to add a new column `new`

with conditional row values as follows:

If a row from `id`

== `id1`

, then the new row is `id1 is cat 1`

If a row from `id`

== `id2`

, then the new row is `id2 is cat 2`

If a row from `id`

== `id3`

, then the new row is `id3 is cat 3`

else, `idx is cat 0`

, where x is the id that is not one of `id1`

, `id2`

, or `id3`

This is what I tried so far. I think the solution should be to wrap the for loop inside a function and use that function with `apply`

and/or `lambda`

.

```
import pandas as pd
df = pd.DataFrame({
'id': ['id1', 'id2', 'id3', 'id8', 'id9']
})
df
dict = {'id1': '1', 'id2': '2', 'id3': '3'}
for k, val in dict.items():
if k == "id1" or k == "id2" or k == "id3" in df['state']:
print(str(k) + " is cat " + str(val))
else:
print(str(k) + " is cat 0")
```

Desired result:

```
id new
id1 id1 is cat 1
id2 id2 is cat 2
id3 id3 is cat 3
id8 id8 is cat 0
id9 id9 is cat 0
```

### >Solution :

You can get number and save in `m`

then use `numpy.where`

and if number `m.isin(['1','2','3'])`

use number of `m`

else use `0`

.

```
import numpy as np
m = df['id'].str[2:]
tf = m.isin(['1','2','3'])
df['new'] = np.where(tf,
df['id'] + " is cat " + m ,
df['id'] + " is cat 0")
print(df)
```

Output:

```
id new
0 id1 id1 is cat 1
1 id2 id2 is cat 2
2 id3 id3 is cat 3
3 id8 id8 is cat 0
4 id9 id9 is cat 0
```