How to work with dataset without column names?

Question

I have a dataset of 2 columns as follows a 1 b 2 c 3

That dataset doesn't have names for both columns, how should I use select to work on it, i.e., get data with the second column number bigger than 2

myDataset[Select[#2>2]]  doesn't work,   How to refer the second column?

thanks in advance

Szabolcs · Accepted Answer · 2017-05-14 20:47:42Z

3

Two mistakes:

The function must end in &
A whole row of the dataset will be passed to that function as a list, so use #[[2]] > 2& instead of #2 > 2&.

answered May 14, 2017 at 20:47

Szabolcs

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Fierce82 · Accepted Answer · 2017-05-15 07:34:22Z

Try this:

define your data, let's say:

myData = {{a, 1}, {b, 2}, {c, 3}, {d, 5}, {e, 45}, {f, 2}, {g, 3}}

{{a, 1}, {b, 2}, {c, 3}, {d, 5}, {e, 45}, {f, 2}, {g, 3}}

In order to get second column

myData[[All, 2]]

{1, 2, 3, 5, 45, 2, 3}

So, your query should be something like this:

Select[myData[[All, 2]], # > 2 &]

{3, 5, 45, 3}

If you need their position, you can use this (credits to J.M., who also suggests Flatten should you need to manipulate somehow your results:

Position[myData[[All, 2]], _?(# > 2 &)]

{{3}, {4}, {5}, {7}}

2 Answers 2