# Find an element in a list of tuples

## Question:

I have a list ‘a’

```
a= [(1,2),(1,4),(3,5),(5,7)]
```

I need to find all the tuples for a particular number. say for 1 it will be

```
result = [(1,2),(1,4)]
```

How do I do that?

## Answers:

If you just want the first number to match you can do it like this:

```
[item for item in a if item[0] == 1]
```

If you are just searching for tuples with 1 in them:

```
[item for item in a if 1 in item]
```

Read up on List Comprehensions

```
[ (x,y) for x, y in a if x == 1 ]
```

Also read up up generator functions and the `yield`

statement.

```
def filter_value( someList, value ):
for x, y in someList:
if x == value :
yield x,y
result= list( filter_value( a, 1 ) )
```

```
for item in a:
if 1 in item:
print item
```

```
[tup for tup in a if tup[0] == 1]
```

There is actually a clever way to do this that is useful for any list of tuples where the size of each tuple is 2: you can convert your list into a single dictionary.

For example,

```
test = [("hi", 1), ("there", 2)]
test = dict(test)
print test["hi"] # prints 1
```

The `filter`

function can also provide an interesting solution:

```
result = list(filter(lambda x: x.count(1) > 0, a))
```

which searches the tuples in the list `a`

for any occurrences of `1`

. If the search is limited to the first element, the solution can be modified into:

```
result = list(filter(lambda x: x[0] == 1, a))
```

Using filter function:

>>> def get_values(iterables, key_to_find):

return list(filter(lambda x:key_to_find in x, iterables)) >>> a = [(1,2),(1,4),(3,5),(5,7)] >>> get_values(a, 1) >>> [(1, 2), (1, 4)]

```
>>> [i for i in a if 1 in i]
```

[(1, 2), (1, 4)]

Or `takewhile`

, ( addition to this, example of more values is shown ):

```
>>> a= [(1,2),(1,4),(3,5),(5,7),(0,2)]
>>> import itertools
>>> list(itertools.takewhile(lambda x: x[0]==1,a))
[(1, 2), (1, 4)]
>>>
```

if unsorted, like:

```
>>> a= [(1,2),(3,5),(1,4),(5,7)]
>>> import itertools
>>> list(itertools.takewhile(lambda x: x[0]==1,sorted(a,key=lambda x: x[0]==1)))
[(1, 2), (1, 4)]
>>>
```

if you want to search tuple for any number which is present in tuple then you can use

```
a= [(1,2),(1,4),(3,5),(5,7)]
i=1
result=[]
for j in a:
if i in j:
result.append(j)
print(result)
```

You can also use `if i==j[0] or i==j[index]`

if you want to search a number in particular index