Python：如何从列表中删除化合价低于特定值的值

Question

在 ArcGis 中，我想计算我绘制的道路网络的连通性。因此，我根据彼此相交的街道数量为每个道路交叉口赋予价。但是，在当前情况下，工具箱还将包括两条线（例如，一条曲线），它们以 2 的化合价相互连接。我需要删除列表中化合价 < 3 的所有值，但由于我几乎没有编程经验，我不知道如何正确地做到这一点。下面是工具箱中用于计算顶点层的一段代码。

#----------------------------------
#Begin of calculating valence field
gp.addmessage("Begin of calculating valence field")
#----------------------------------

#Make layer of vertices
#----------------------
gp.addmessage("Make layer of vertices")
desc=gp.Describe(inline)
shapefieldname = desc.ShapeFieldName
thesr=desc.SpatialReference
gp.CreateFeatureClass(gp.workspace,vert, "Point","", "ENABLED", "DISABLED", thesr)
gp.addfield(vert, "valence", "short")
listk=[]
rows=gp.SearchCursor(inline) 
row = rows.Next()
while row:
    feat = row.GetValue(shapefieldname)
    partnum=0
    partcount=feat.PartCount
    print partcount
    while partnum < partcount:
        part = feat.GetPart(partnum)
        pnt = part.Next()
        pntcount = 0
        thex=pnt.x
        they=pnt.y
        thekey=(thex*1000000)+they
        while pnt:
            if thekey not in listk:
                cur = gp.InsertCursor(vert)
                rowvert = cur.NewRow()
                rowvert.shape = pnt
                cur.InsertRow(rowvert)
                listk.append(thekey)
            pnt = part.Next()
            pntcount += 1
        partnum += 1
    row=rows.next()
del row, rows, cur

# Remove all values valence < 3
#-------------------------------

Answer 1

在你的情况下，我会创建一个新列表，只包含化合价 >= 3:

my_list = [1, 12, 4, 3, 7, 2, 0]
filtered_list = [val for val in my_list if val >= 3]
print filtered_list  # displays [12, 4, 3, 7]

Answer 2

可以使用过滤功能

 >>>filter(lambda x : x>3 , [1,2,3,4,5])
 [4,5]

Answer 3

在 Python 中，如果您有一个值列表，您可以执行此操作

# Generate a random list for example.
import random
some_list = random.sample(range(30), 4)

# Keep elements greater than 3.
filtered_list = [value for value in some_list if value >= 3]

# The same outcome, another way to write it.
filtered_list = filter(lambda x: x >= 3, some_list)

# The same outcome, but written as a loop.
filtered_list = []
for value in some_list:
    if value >= 3:
        filtered_list.append(value)

自从我使用 ArcGIS/arcpy 以来已经有一段时间了，但我很确定 FeatureClasses 不能像普通 Python lists. Regarding your arcpy code, you could use an UpdateCursor 那样简单地处理删除行：

# Create an empty FeatureClass from the original.
with arcpy.UpdateCursor(your_feature_class) as rows:
    for row in rows:
        if row.valence <= 2:
            rows.deleteRow(row)

Python：如何从列表中删除化合价低于特定值的值

Python: How to remove values from a list that have a valence lower than a certain value

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