I have the following dataset which is a **.json** file: [![enter image description here][1]][1] and I would like to get the first word for every string inside `lista_asm`, so I would like to get: jmp,push,uncomisd,...etc what I am doing to do this is the following: dataFrame['opcodes'] = dataFrame['lista_asm'].apply(lambda x:[i.split()[0] for i in x]) but it gives me back the following error message: 3589 else: 3590 values = self.astype(object).values -> 3591 mapped = lib.map_infer(values, f, convert=convert_dtype) 3592 3593 if len(mapped) and isinstance(mapped[0], Series): pandas/_libs/lib.pyx in pandas._libs.lib.map_infer() <ipython-input-18-5506b5721bf1> in <lambda>(x) ----> 1 dataFrame['opcodes'] = dataFrame['lista_asm'].apply(lambda x:[i.split()[0].strip() for i in x]) IndexError: list index out of range I don't understand what is wrong. Can somebody please help me? [EDIT]Trying the code: dataFrame['opcodes'] = dataFrame['lista_asm'].apply(lambda x:x[0].split(" ",2)[0]) and adding : df = dataFrame[["opcodes", "semantic"]].copy() df I get: [![enter image description here][2]][2] what I would like to get is a list of the type **[push,mov,..]** and this for every row. It seems like when I do `x[0]` it does not return the first element of the list, but returns the pharentesis, which is weird. Am I doing something wrong which I don't see? [1]: https://i.sstatic.net/BZqbC.png [2]: https://i.sstatic.net/wzs25.png