array alice of [:-0] ??

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  • guthrie
    #1

    array alice of [:-0] ??

    Beginner question! :-)

    x=[1,2,3,4]
    for i in range(len(x)):
    print x[:-i]
    >>[]
    >>[1,2,3]
    >>[1,2]
    >>[1]
    1) The x[:-0] result seems inconsistent to me;
    I get the idea that -0=0, so it is taken as x[:0] -[]
    2) how then should one do this basic left-recursive subsetting (easily).

    Thanks.


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    • John Machin
      #2
      Re: array alice of [:-0] ??

      On 18/07/2006 11:17 PM, guthrie wrote:
      Beginner question! :-)
      >
      x=[1,2,3,4]
      for i in range(len(x)):
      print x[:-i]
      >
      >>[]
      >>[1,2,3]
      >>[1,2]
      >>[1]
      >
      1) The x[:-0] result seems inconsistent to me;
      I get the idea that -0=0, so it is taken as x[:0] -[]
      2) how then should one do this basic left-recursive subsetting (easily).
      >
      >
      |>for i in range(len(x), -1, -1):
      .... print x[:i]
      ....
      [1, 2, 3, 4]
      [1, 2, 3]
      [1, 2]
      [1]
      []

        Comment

        • Boris Borcic
          #3
          Re: array alice of [:-0] ??

          guthrie wrote:
          Beginner question! :-)
          >
          x=[1,2,3,4]
          for i in range(len(x)):
          print x[:-i]
          >
          >>[]
          >>[1,2,3]
          >>[1,2]
          >>[1]
          >
          1) The x[:-0] result seems inconsistent to me;
          I get the idea that -0=0, so it is taken as x[:0] -[]
          that's what you get.
          2) how then should one do this basic left-recursive subsetting (easily).
          I am not sure what you mean, but replacing x[:-i] by x[:len(x)-i] you will get
          continuous behavior at i==0.

            Comment

            • Antoon Pardon
              #4
              Re: array alice of [:-0] ??

              On 2006-07-18, guthrie <guthrie@mum.ed uwrote:
              Beginner question! :-)
              >
              x=[1,2,3,4]
              for i in range(len(x)):
              print x[:-i]
              >
              >[]
              >[1,2,3]
              >[1,2]
              >[1]
              >
              1) The x[:-0] result seems inconsistent to me;
              I get the idea that -0=0, so it is taken as x[:0] -[]
              That is correct. Negative indexes are a handy shorthand, but
              they can give unexpected/strange results in a number of cases.
              2) how then should one do this basic left-recursive subsetting (easily).
              x=[1,2,3,4]
              lng = len(x)
              for i in range(lng):
              print x[:lng-i]

              --
              Antoon Pardon

                Comment

                • guthrie
                  #5
                  Re: array slice of [:-0] ??

                  Thanks all!!
                  ---------------------

                  guthrie wrote:
                  Beginner question! :-)
                  >
                  x=[1,2,3,4]
                  for i in range(len(x)):
                  print x[:-i]
                  >
                  >>[]
                  >>[1,2,3]
                  >>[1,2]
                  >>[1]
                  >
                  1) The x[:-0] result seems inconsistent to me;
                  I get the idea that -0=0, so it is taken as x[:0] -[]
                  2) how then should one do this basic left-recursive subsetting (easily).
                  >
                  Thanks.
                  >

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                    Comment

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