How to remove an element from a nested list?

Question

if I have a nested list such as:

m=[[34,345,232],[23,343,342]]

if I write m.remove(345) it gives an error message saying the element is not in the list.

I want to know how to remove an element from the nested list, easily.

Answer 1

In [5]: m=[[34,345,232],[23,343,342]]

In [7]: [[ subelt for subelt in elt if subelt != 345 ] for elt in m] 
Out[7]: [[34, 232], [23, 343, 342]]

Note that remove(345) only removes the first occurrance of of 345 (if it exists). The above code removes all occurrances of 345.

Answer 2

There is no shortcut for this. You have to remove the value from every nested list in the container list:

for L in m:
    try:
        L.remove(345)
    except ValueError:
        pass

If you want similiar behavior like list.remove , use something like the following:

def remove_nested(L, x):
    for S in L:
        try:
            S.remove(x)
        except ValueError:
            pass
        else:
            break  # Value was found and removed
    else:
        raise ValueError("remove_nested(L, x): x not in nested list")

Answer 3

If you have more than one nested level this could help

def nested_remove(L, x):
    if x in L:
        L.remove(x)
    else:
        for element in L:
            if type(element) is list:
                nested_remove(element, x)

>>> m=[[34,345,232],[23,343,342]]
>>> nested_remove(m, 345)
>>> m
[[34, 232], [23, 343, 342]]

>>> m=[[34,[345,56,78],232],[23,343,342]]
>>> nested_remove(m, 345)
>>> m
[[34, [56, 78], 232], [23, 343, 342]]

Answer 4

i=0
for item in nodes:
    for itm in item:
        m=database_index[itm]
        print m
        if m[1]=='text0526' or m[1]=='text0194' or m[1]=='phone0526' or m[1]=='phone0194':
            nodes[i].remove(itm)
    i+=1

this i how i solved my problem by using a variable i to save the above level of the nested list.

Answer 5

If you want to remove only by indexes you can use this method

m[0].pop(1)

by this you can specify only the index. This is helpful if you know only the position you want to remove.

Answer 6

您可以使用此代码删除 345。

m[0].remove(345)

Answer 7

You can delete by using delete:- del m[1][1] or by using below code

for i in m:
    for j in i:
        if j==345:
            i.remove(j)
print(m)

Answer 8

A shortcut of doing this is using del command:

del list[element] element[nested element] 

del [] []

Answer 9

If you have the same item (ie 345) in more places to remove from the nested list, you can try:

for x in m:
    for index in range(len(x) -1, -1, -1):
        if x[index] == 345:
            del x[index]
    print(x)

or

for x in m:
    for z in x:
        if z != 345:
            print(z)