Structuring a 2D array from a pandas dataframe

IIUC, you can do something like:

n=2 #change this as you like for no. of splits
s=df.Text.dropna().reset_index(drop=True)
c=s.groupby(s.index//n).cumcount().eq(0).shift().shift(-1).fillna(False)

---

[[i] for i in s.groupby(c.cumsum()).apply(' '.join).tolist()]

---

[['Hi this is'], ['just a'], ['single sentence.'], 
    ['This is another one.'], ['This is a'], ['third sentence .']]

EDIT:

d=dict(zip(df.loc[df.Text.notna(),'Text'].index,c.index))
ser=pd.Series(d)
df['new']=ser.reindex(range(ser.index.min(),
                        ser.index.max()+1)).map(c).fillna(False).astype(int)
print(df)

---

               Text  Selection_Values  new
0                Hi                 0    1
1           this is                 0    0
2              just                 0    1
3                 a                 0    0
4            single                 0    1
5         sentence.                 1    0
6              This                 0    1
7               NaN                 0    0
8   is another one.                 1    0
9           This is                 0    1
10                a                 0    0
11            third                 0    1
12         sentence                 0    0
13                .                 0    0

Here is a rather long, and bulky code, but it does the job! :)

selection_values = df["Selection_Values"].tolist()    
max_number_of_cells_per_list = 3
a = [[s.str.cat(sep=' ')] for s in np.split(df.Text, df[df.Selection_Values == 1].index+1) if not s.empty]
print(a)

number_of_cells = 0
j = 0
for i in range(len(df['Text'])):
    if isinstance(df['Text'][i], str): 
        number_of_cells += 1



    if df["Selection_Values"][i] == 1 or i == len(df['Text'])-1:

        print("j: ", j)
        if number_of_cells > max_number_of_cells_per_list:
            print(number_of_cells,max_number_of_cells_per_list)
            print("\nmax number of cells reached")
            n = np.ceil(np.divide(number_of_cells,max_number_of_cells_per_list))
            print("deviding into ", n, " cells")
            add = int((i-j)/n)
            print("add", add)
            for k in range(int(n)):

                if k == n-1:
                    j = i
                else:
                    j += add
                print("j: ", j)
                selection_values[j] = 1
            print("\n")

        # Reset Cell Counter Every time a new list should start        
        number_of_cells = 0
        j = i


df['Selection_Values'] = selection_values
print("\n", df)


a = [[s.str.cat(sep=' ')] for s in np.split(df.Text, df[df.Selection_Values == 1].index+1) if not s.empty]
print(a)

You get:

               Text  Selection_Values
0                Hi                 0
1           this is                 0
2              just                 0
3                 a                 0
4            single                 0
5         sentence.                 1
6              This                 0
7               NaN                 0
8   is another one.                 1
9           This is                 0
10                a                 0
11            third                 0
12         sentence                 0
13                .                 0
[['Hi this is just a single sentence.'], ['This is another one.'], ['This is a third sentence .']]
j:  0
6 3

max number of cells reached
deviding into  2.0  cells
add 2
j:  2
j:  5


j:  5
j:  8
5 3

max number of cells reached
deviding into  2.0  cells
add 2
j:  10
j:  13



                Text  Selection_Values
0                Hi                 0
1           this is                 0
2              just                 1
3                 a                 0
4            single                 0
5         sentence.                 1
6              This                 0
7               NaN                 0
8   is another one.                 1
9           This is                 0
10                a                 1
11            third                 0
12         sentence                 0
13                .                 1
[['Hi this is just'], ['a single sentence.'], ['This is another one.'], ['This is a'], ['third sentence .']]