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Data.Table and Pandas
Published in Nailong Zhang, A Tour of Data Science, 2020
What is the key in a data.table? We have talked about RDBMS and SQL in the previous section. With select from where we can easily access specific rows satisfying certain conditions. When the database table is too large, a database index is used to improve the performance of data retrieval operations. Essentially, a database index is a data structure, and to maintain the data structure, additional cost (for example, space) may be required. The reason to use key in data.table and index in pandas is very similar. Now let’s see how to set key and index.
Multilayer Antireflection Theory
Published in Andrew Sarangan, Optical Thin Film Design, 2020
This description of how the absentee layer improves the antireflection performance is somewhat qualitative. It does not give us the exact refractive index for the absentee layer, nor the spectral width of the antireflection band. All we can say is that the refractive index of the absentee layer has to be larger than the effective reflectance index of the substrate with the first layer. It is equally important that the index not be too high either. A spacer with too large an index will move the end point in the opposite direction away from 1.0. This will have the effect of reducing the antireflection bandwidth. The optimum value has to be determined to some extent by trial and error. Nevertheless, this description does provide an understanding of how the absentee layer works and an approximate value of its refractive index. On the other hand, instead of the HL, if the layer sequence is LH (which is rare in most practical scenarios), the absentee index has to be lower to achieve the desired result.
PRAs and environmental issues
Published in Owain Johnson, The Price Reporters, 2017
BNEF publishes the Wind Turbine Price Index, which is an index of the price of wind turbines on delivery and an outlook for the next 24 months, and the Solar Spot Price Indexes, which are weekly pricing updates, as well as the Solar Shipments Index, which is a monthly reference point for shipments from major Chinese and Taiwanese cell and module makers. Bloomberg again relies upon a survey methodology to derive its indices, whereby panel members submit assessments that are then reviewed by analysts and prices that are more than 50 per cent away from the average are rejected. The indices are updated daily, although the official spot index is provided on a weekly basis.
BTLA-LSDG: Blockchain-Based Triune Layered Architecture for Authenticated Subgraph Query Search in Large-Scale Dynamic Graphs
Published in IETE Journal of Research, 2023
G. Sharmila, M. K. Kavitha Devi
Wan et al. [32] attempt to approximate query processing on large-scale knowledge graphs. It is referred to as LKAQ and this scheme is enabled to control the trade-off between in-memory usage and accuracy. In this paper, authors developed two kinds of indexes: M-index and I-index. It is very complex when an approximate query is given. Individual index construction requires more storage space. A balanced multiway multidimensional indexing tree is proposed [33] in the application of Peer-to-Peer (P2P). This index structure is suited for complex query processing. A tree traversal for the adjacency nodes can be in the following: (1). Traverse the first subtree in Inorder, (2). Traverse the node and (3). Traverse the residual subtree in Inorder. Time complexity and space complexity are very large.
Efficiently identifying closed roads by integrating and indexing open data
Published in Journal of the Chinese Institute of Engineers, 2021
Ya-Hui Chang, Shu-Han He, Chih-Wei Tseng
Index structures are used to improve the querying efficiency. Many indices in addition to R-trees have been designed for spatial data, such as the Quadtree structure proposed by Finkel and Bentley (1974). The R-tree structure usually outperforms others in that it is a balanced tree and can provide stable accesses most of the time, but it is time consuming to build an optimal one. Beckmann et al. (1990) proposed the R*-tree to incorporate a combined optimization of areas, margins and overlaps of each enclosing rectangle of the inner node. Ang and Tan (1997) focused on the efficiency of the construction process and discussed a better linear algorithm to split the node. The R-tree index is currently widely applied in many spatial operations and for handling geographical data. To name a few, Schubert, Zimek, and Kriegel (2013) discussed how to apply it in geodetic distance queries. Chang, Lee, and Ke (2019) discussed how to represent flooded areas properly in the R-tree for future efficient querying. Since the flooded areas have irregular shapes due to geographical characteristics, the authors advocated the idea of partitioning the MBRs into smaller rectangles for better performance.
A power quality evaluation method for distribution system with renewable energy
Published in International Journal of Electronics, 2020
Jinxin Chen, Guobing Pan, Jing Ouyang, Libin Zhang
Figure 8. shows that the comprehensive evaluation value of the power quality with different index factors. When the was 0.583 or 0.667, the effect of the index factor was weak, and the evaluation value of the time zone 2 was lower than the zone 5. When the was 0.750, 0.833 or 0.917, the effect of the time factor becomes weaker, and the evaluation value of the zone 2 catches up with zone 5. We find that the larger , the greater difference between the final evaluation values. However, if the index factor was too large, the better index will be overemphasised and the worse will be ignored. The comprehensive evaluation value of time zone 2 and time 5 shown in Table 2.