Delete rows of a matrix that do not satisfy a certain condition?

Questions
1

Hello. I generate a matrix of outcomes. Suppose we have 10,20,30 values. I need to delete unnecessary rows of the matrix. My idea is to multiply 10 by the second column, 20 by third column, 30 by fourth column. After that I delete all rows which do not satisfy the condition. for n-1, we remove all rows where an element has the value more than 30, for n-2 more than 50, for n-3 more than 60. But I can’t even get 10,20,30 multiplied to second, third and fourth columns. Please, help me. Thanks in advance!

Regards,

Alex

outcomes2.nb (15.7 KB)

2

Well I make some progress, the only questions I have now. How to delete rows which are more 60(forth column)?

{"0", "0", "0", "0"},
{"10", "0", "0", "10"},
{"0", "20", "0", "20"},
{"0", "0", "30", "30"},
{"20", "0", "0", "20"},
{"0", "40", "0", "40"},
{"0", "0", "60", "60"},
{"10", "0", "0", "10"},
{"0", "20", "0", "20"},
{"0", "0", "30", "30"},
{"30", "0", "0", "30"},
{"0", "60", "0", "60"},
{"0", "0", "90", "90"},
{"20", "20", "0", "40"},
{"20", "0", "30", "50"},
{"10", "40", "0", "50"},
{"10", "0", "60", "70"},
{"0", "40", "30", "70"},
{"0", "20", "60", "80"},
{"10", "20", "30", "60"}
3

Alex,

Look at Select[].

If your lst is numbers and not strings:

Select[lst, #[[4]] <= 60 &]

Regards,

Neil

4

Thank you so much for your reply. Could you please give me another hint on how to delete each forth element from the list.

{{0, 0, 0, 0}, {10, 0, 0, 10}, {0, 20, 0, 20},
mat12 = Delete[lst, 4]

This comand dosent work in this case.

5

And how to add a column to specific place, for example, in the middle.
,this adds a column to the end

MapThread[Append , {sr11, Table[0, Length[sr11]]}] Insert dosent work for this case

Regards,

6

Alex,

You need to Map the Delete:

Delete[4] /@ lst

or

Map[Delete[4], lst]

Regards,

Neil

7

Alex,

There is extensive documentation on adding and taking rows and columns of matrices. Look at the part options and the matrix and vector operations guide.

For example,

lst[[All, 2]]

Is the second column. You can also set the second column with

lst[[All, 2]] = {....}