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## Unpack nested column in table

New Contributor III

hi, how can we unpack nested column in a table? Thanks.

e.g. t:flip `a`b!((1 2 3);((4 5 6);(6 12 23);)(12 36 14)))

to t: flip `a`b1`b2`b3!((1 2 3);(4 6 12);(5 12 36);(6 23 14))

7 REPLIES 7
New Contributor

Not too sure on a more elegant and generalisable way, but this code will produce the desired result:

(flip enlist[`a]!enlist[t `a]),'flip `b1`b2`b3!t `b

New Contributor III

I guess you mean:

``````(flip enlist[`a]!enlist[t `a]),'flip `b1`b2`b3!flip t `b

a b1 b2 b3

----------

1 4  5  6

2 6  12 23

3 12 36 14``````

New Contributor III

select a:a ,b1:b[;0],b2:b[;1],b3:b[;2] from t

a b1 b2 b3

----------

1 4  5  6

2 6  12 23

3 12 36 14

New Contributor

Another option: flip `a`b1`b2`b3!flip raze each t

New Contributor

Its a little slower, but generalizes the solution a bit.

``````func:{[td]
c:where 0=type each flip td; / find which columns need unpacked
ocn:cols td; / store all original column names for oder
ncn:`\$raze{string[x],/:string 1+til count first each flip[y]x}[;td]each(),c; / calculate new column names
acn:ncn,ocn except c; / list of all final columns
c:raze {x where x like y}[acn;]each string[ocn],'"*"; / all final columns in order

flip c!flip raze each td / create final table with column names and column data
}

q)t
a b
----------
1 4  5  6
2 6  12 23
3 12 36 14
q)func t
a b1 b2 b3
----------
1 4  5  6
2 6  12 23
3 12 36 14
q)t3
a b        c d
------------------
1 4  5  6  1 1 2 3
2 6  12 23 2 4 5 6
3 12 36 14 3 7 8 9
q)func t3
a b1 b2 b3 c d1 d2 d3
---------------------
1 4  5  6  1 1  2  3
2 6  12 23 2 4  5  6
3 12 36 14 3 7  8  9``````
New Contributor III

A generalized solution that doesn't use hardcoded column names (provided as input) or assume the the cells in the nested column having the same length (padded with null for those with shorter length).

``````unpack:{[t;c]
maxLen:max count each t[c];
newCols:`\$string[c] ,/: string 1+til maxLen;
// concatenate the parts other than the specified column, with the unpacked parts
// (x;::;y) is the parsed form of x[;y]
![t; (); 0b; enlist c] ,' ?[t; (); 0b; newCols!{(x;::;y)}'[c;til maxLen]]
}``````

Valued Contributor

Assume here the column value is a matrix. Start with the new column names.

``````q)show ncn:`\$string[`b],/:string 1+til count first t`b
`b1`b2`b3``````

Pair them with the matrix columns.

``````q)show d:ncn!flip t`b
b1| 4 6  12
b2| 5 12 36
b3| 6 23 14``````

Here’s the table with the nested column removed. (We use Functional qSQL rather than hard-code the column name.)

``````q)show twc:![t;();0b;enlist`b]  / table without column
a
-
1
2
3

q)twc,'flip d  / Join Each new tuple
a b1 b2 b3
----------
1 4  5  6
2 6  12 23
3 12 36 14``````

Putting it together:

``````un:{[tbl;col]                                  / un-nest col in tbl
mat:flip tbl col;                              / un-nest column
ncn:`\$(,/:) . string(col;) 1+til count mat;    / new column names
![tbl;();0b;enlist col],'flip ncn!mat }``````
``````q)un[t;`b]
a b1 b2 b3
----------
1 4  5  6
2 6  12 23
3 12 36 14``````