# J: A convenient method for entering a matrix?

I have an n-by-m matrix written on paper and I want to do calculations on it in J.

I can enter matrices like this (n = 3, m = 3):

```
A =: 3 4 $ 1 3 2 4 7 8 1 2 2 0 0 1
```

The question is how to introduce a matrix like this:

```
A =: (something here)
1 3 2 4
7 8 1 2
2 0 0 1
)
```

The reason I am asking such a strange question is because I have seen in some book a similar method for typing matrices using a verb `0 : 0`

or something similar, but I cannot remember where. **: {**

source to share

Using a dyadic (rather than monadic) `".`

will try to resolve each string as a string of numbers, rather than evaluate it as a J-sentence. If the string cannot be resolved to a number, the left argument is used instead ( `_99`

in the example below). This approach will correctly interpret a larger set of numbers represented as strings.

Choice `noun define`

, rather than `0 : 0`

just storing the set of brackets that would otherwise be needed to split `_2`

by `0`

.

```
]A =: _99&".;._2 noun define
1 -3 2 4
7 8 1 2
2 0 0 1
)
1 _3 2 4
7 8 1 2
2 0 0 1
```

source to share